PC won't boot but fan spins for 3 seconds then stops

Hi. The motherboard is an Aus P5GD1-VM.
The case didn't come with a pwer supply, so it's the original supply I'm using.  RAM has been checked and there are no other cards attached.
The motherboard was originally mounted on little hex shaped mountings, but they wouldn't allow the motherboard to fit in the new case as the sockets on the back (mouse, keyboard etc) wouldn't have aligned. The case has raised sections that are the mounting points, so I mounted it on these without the hex mountings. I guess that is metal against metal, so should there be some sort of insulating washer or something between the board and case?

What's the make/model of the new case??

You can also test the psu to eliminate that. If you have a working one, just swap them out and try it. If not:
There are power supply testers out there like this one:  http://www.pcper.com/article.php?aid=246
Or you can make sure there's a load on the power supply such as hard drive and test it with a mutltimeter.  If the board powers up you can leave the psu plugged into the board and test from the backside of the atx plug. If the machien will not power on, just short the green and black wires while the hard drive is plugged in for load, this can be done with a paperclip.  That turns the power supply on, now test the following wires for dcv in the ranges listed.

Red, purple, and grey:  4.75 to 5.25 VDC
Yellow: 11.4 to 12.6 VDC
Orange: 3.17 to 3.4 VDC
White: -5.5 to -4.5 VDC (negative)
Blue: -13.2 to -10.8 VDC (negative)

Hope this is helpful,
Jappo

Hi guys

Haven't had a moment to check any of this but having read all your comments I suspect that the board is shorting out because it's in contact with the case. The case did come with some little red washers (sorry, I'm normally more technical than that!) and some plastic plugs with screw threads. I think the washers are the way to go, but I presume they go between the screw and the motherboard, rather than between the board and the case, as the latter would be more difficult to fit. If that's right then surely the screws are still in contact with the case - or is the solder around the mounting holes not connected to anything electrically?

Thanks again.

Those "... plastic plugs with screw threads ..." are almost certainly your standoffs.   Not sure what the washers are, but they're probably not used for motherboard mounting.

The mounting holes are all connected electrically to ground ==> so the screws simply provide additional grounding to the case.

... from what you've described, it's almost certain that your problem here is simply that you've not mounted the motherboard correctly.   Hopefully the shorts that were induced as a result haven't damaged the board ==> most likely they have not, but you'll know soon enough :-)

Be sure you only mount standoffs at the right places for YOUR motherboard ==> the case will have more places for standoffs than your motherboard uses ... you only want to mount standoffs where there are mounting holes on the motherboard.

... also, as I asked earlier, did you use the ATX connector plate for YOUR motherboard in the new case??

Hi guys

Completely confused now! I am using the correct ATX plate and I don't know the make of case. I can't fit the brass standoffs because the mounting points are little "hills", so that would raise the board too high to fit the ATX plate. If the metal-rimmed screw holes are to ground the board via the screws, then why do I have plastic standoffs? They won't conduct! And they'd probably make it too high as well, although not as high as the brass standoffs (which presumably don't conduct?).  I've separated the board from the case with cardboard, and it boots fine, so luckily I've not blown anything up. So if that works, why does the board need to be earthed to the case?

:(

The board does not have to be grounded to the case, it's a good practice, but you should get good conductivity ground thru the rear plate as well as any pci cards that you install. The psu is also grounding the board thru the power plug. Grounding the board to the case is just good practice to eliminate any grounding issues.  You can build a computer in a wooden box and still not have problems.
  Obviously you discovered that the board needs to be seperated in some fashion from the case.  And since a picture is worth a thousand words, is there any chance you can take a couple of digital pics, save them as jpg and upload them to www.ee-stuff.com    Then post a link to them here, take a pick of the case on the inside, and pics(closeup) of the standoffs both brass and plastic that you have and that way we can get a better idea of what you have and make the proper suggestions. I've not found a case that standoffs won't fit in, but obviously there are too many of them out there for me to have experienced them all.
Jappo

Your case almost certainly came with some standoffs ==> they are usually brass and DO conduct electrically ... they simply provide additional grounding of the motherboard to the case (in addition to that provided by the power supply grounds & ATX connector plate).

It's not clear what you're describing here ... pictures (as suggested above) would be a good idea.   But if, in fact, the case simply has raised mounting points; then you need to install insulators (perhaps the washers you described) on any of those points that do NOT match the motherboard's mounting holes.

The problem here was CLEARLY an improperly mounted motherboard ==> you just need to determine exactly how your case is designed to accomodate the motherboard.

ATX cases are fairly standardized as far as mounting is concerned. As Gary mentioned, check that every one of those raised mounting points that are under the motherboard line up with a mounting hole in the motherboard. If one is touching the motherboard where no hole is present, a short will occur. Do not insert brass standoffs where no motherboard mounting hole is present.
The plastic type of standoff is usually used when a board needs support under the board and no hole is available in the motherboard.

I think I've discovered the problem. Looks like the laws of physics don't actually apply any more in the south of England! Wish I knew that before....

I'm doing this for a friend (never again) and the shop he bought the case from say they fit these cases daily and the board goes straight onto the raised mountings which take the place of those brass hex standoffs. Everything is connected as it was in the old case - I took notes and drew sketches. I can't get my camera to work because the battery is flat and I can't find the ****** charger (probably only exists in a parallel universe now, thanks to the revocation of physical law) so I can't show you what's going on. Unless anyone knows how to make the laws of physics work properly I think I have only one choice - give it back to my mate partially built and let him take it back to the shop and say "go on then, clever clogs, make this one work!!". I'm open to other ideas as well  though...

Well living in a parallel universe makes physics a completely different study... I'm afraid without some sort of visual, I'm not going to be of much help to you.
Sorry about that.
Jappo

Assuming the shop is telling you the truth ...  (this is a very unusual case if so) ...

The "raised mountings" would be fine IF they exactly match the mounting holes on the motherboard.   Chances are there are some of those "raised mountings" at other locations ... and that's what's causing the shorts that are keeping the system from working.

Look VERY carefully at the location of the mounting holes on the motherboard vs. the location of the "raised mountings."   Anywhere there's a "raised mounting" that doesn't match a hole in the motherboard, cover it with black electrical tape (so there's no conductivity at that point).
(a couple of strips to be sure would be good)

If you mount the board like that it will most likely work just fine.

OK.... there are six raised mounting points. Each correspond to a hole on the motherboard, all of which have metal around them. I have 5 cardboard washers, so I chose one mounting point to cover with insulation tape, as suggested, and used the cardboard washers on the screws for the other 5 holes so that they are between the board and screw. This, I thought, would stop the screws from grouding the board to the case. Still won't boot. Fan still spins for a second then gives up. Could the case be faulty?

I would cover all the mount points with tape and then screw the motherboard down. The screws do not need to be isolated as the solder pads they come in contact with on the top of the motherboard are grounded. The mounts underneath may be touching a part of the motherboard that is causing the problem,so covering the with tape may keep this from happening.

Hi guys, I've solved it. Photos would not have helped you!

It turns out there's a huge piece of wire/solder sticking out the bottom of the board (about 3mm long) which I'd missed - I think I assumed it was plastic as it's close to the CPU fan lugs which also go right through the board. Brass standoffs (which the old case had) are longer than this so it wasn't a problem in the old case, but the new case's built in mounting points are shorter than these (just). That 3mm was enough to short it out. I covered the area with tape but the wire was so sharp it cut right through and so didn't sort it out. In the end I drilled a hole in the backplate where the wire was touching it. It's a bit of a rough hole, but it has done the job.

Big, big, big thanks to all of you for your help and suggestions. This problem has been driving me crazy for over a week and everything each of you suggested has helped and ultimately got the issue resolved. No one person could possibly have known about the stray wire, so the points cannot all go to one expert. I am therefore increasing the points and dividing them up as below.

garycase      150 for most suggestions and ultimately concluding it was a mounting issue
sparkmaker   100 for next most suggestions and teaching me a bit about putting a PC together
riteheer           50 for kind efforts. I couldn't follow all your suggestions through but I'm very grateful!

I hope you all see this as fair. Thanks again.
Dave.

Glad it's working ... not surprised it was a shorting issue ==> but a protruding wire was definitely not a "usual" problem :-)

davidcowlerDate,
REally glad you got it working, your persistence in solving the problem is what really paid off.  
Sounds like a poor solder job, and very unusual.
Jappo
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