PC loses power, I hear 2-tone whine/hum from motherboard

>>  Why would one PSU boot it to windows (until it crashes) and two others make it hang on the blue e (until it crashes)?  Why the difference?    <<<  because not all PSU are the same, even if they have the same rating, they may give different spec on the different rails. And the difference can come from aging also.
i recommend to check the power needed here :
http://extreme.outervision.com/psucalculator.jsp      
you may have a bad mobo, or cpu, but test first with a beefier PSU
 

Darn it!  I can never get this kind of heatsink off:
http://static.tigerdirect.com/pdf/MSI_KM4M-L_manual.pdf
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/23986.pdf

I see teh installation tips but NOT The heatsink removal instructions!

Looks like you have to pry the clips outward while pressing DOWN on the clip (pressing down on the clip using the channel exposed after removing the heatsink fan)?  Yeesh...   Dangerous, pushing and prying with point objects, so close to all that circuit board...  Any suggestions?

BACK UP -- Maybe better NOT to remove the heatsink --

I did remove the heatsink fan and YES I did find nickel-sized "pads" of dust blocking the flow into the heatsink. So I removed those and will try to clean the heatsink as well as I can without removing it.

BUT --
Is it always better NOT to remove a heatsink / cpu if you don't have to? Or is it like opening a hood of a car - - nothing bad should happen?

I can imagine cpus getting crushed upon reinsertion of heatsink, or the thermal paste getting pushed to one side so it doesn't do its job anymore, etc. but on the flip side it would be nice to REALLY clean all the little hairs out of all those heatsink walls...

OK, issue solved -- by cleaning the heatsink as you guys told me. I will award points accordingly. I simply cleaned the dust that was accumulated under the heatsink fan, I didn't remove the heatsink.

I added some points for this question because I do want to know the answer to my  questions immediately above (re: (1) the pros or cons of removing the heatsink, and (2) how do you get that brand of heatsink off?)

Normally removing heatsinks isn't a problem. The problem arises with those that originally used thermal pads instead of thermal transfer paste. The thermal pad melts when hot, and then it cools and locks the CPU to the heatsink. When removing the heatsink this will often also pull the CPU along with it out of the locked socket. This will normally not matter much, just don't drop the heatsink with the CPU stuck on it, as that can cause it's pins to bend, then you'd have to straighten them. If the heatsink takes the CPU with it, pry the two apart using a screwdriver. Then remove all the residue of the thermal pad.

Thermal pads and paste age, and therefor either should replaced after some time, or they loose their functionality. Only very little paste should be used, a tiny drop is enough, then it does it's job best and there won't be lots of it oozing out. The heatsink should also be fitted very snuggly on the CPU. CPU's are tough and don't get "crushed". Just make sure you first insert it into it's socket so it fits properly, close the socket's lever, check the CPU holds properly, then firmly reattach the CPU.

Sigh. Guy came to my shop.  THe pc was running fine. Customer took it back home. AT home, the pc dIdn't turn on at all, no lights, no fans, nothing. I brought it back to shop. He's right - it doesn't run at all. I swapped in those other 2 P4 PSU with MATCHING voltages, and it powers up, but again, the process stops on the blue e.

That's really annoying -- the voltages match, but the psu doesn't actually power the unit to windows. So I can't tell the guy for sure if his psu went bad or not, or whether or not a new "matching"(?) psu will fix it. Jeez, how many different brands of PSUs with the exact same voltages / wattaches do you have to keep in your shop, to be able to swap in psus successfully?

Anyway -- I now gotta assume that IN ADDITION to the overheating cpu, his power supply was going bad and therefore was ruined somehow by the fact that I had his PC test-running for a few hours, OR ELSE he banged it on something taking it home (he said he "bumped it"), OR there's something else going on, like with the power button.

Here's one more clue -- before he took it home, just before the last time I got it to go to windows (for the 5 hour test), it would not turn on, until I recabled the power to the psu several times. Then it turned on.

Does that indicate something?  NOTE - NO JUMPERS were changed or messed with at any point. AND the second PSU gets it to power up. So I'm assuming that this whole thing is NOT an issue with the front power button or the jumpers.

I have raised the points to 500. Wasn't sure if I should post this as a new question... the first 350 points will go to the answers alerady given. thx

I would like to also add that if you were to remove the CPU for some reason or another, there is an indication, usually a gold or yellow triangle, on the corner of the CPU that would line up with the socket on Zero Insertion Force socket.  Don't EVER push in these CPU's as you really don't want to bend the pins.  This is kind of irrelevant to the previous question, but while Rindi was there I thought I would just add my two cents about what's further.  You were stating difficulty removing the actual CPU heatsink, on one side of a stock AMD heatsink, there is USUALLY a place on one end of the heatsink retention clip (on the middle tab on the socket) that a #2 flatblade screwdrive will fit.  I carefully use the screwdriver to apply a little force downward towards the board and then away from the socket to free the heatsink.  Just be very careful and don't stab yourself or the board.  Those jokers are on very tight and I have always found it super easy to use this method.  The newer Socket (754 and up to my knowledge) come with this cool locking lever so you don't have to do this.  After that all you have to do is lift the ZIF lever and pull the CPU.  I'm glad your rig is back up and working.

The PSU has a fan in it as well that can grow a carpet and over heat...but that doesn't sound like what you've got.  Check the voltage on the purple wire coming off of the powersupply  on the 20/24 pin connector and you SHOULD have 5 vsb.  If that is there then ohm out the power switch with a multi-meter and see if it closes when you hit the switch (I've never seen these go bad), If you've got the 5 volt stand by, and the switch works, you are throwing power were it needs to go UNLESS you lost a 3 or 12 volt rail.  PSU can be tricky, but I have a tester that makes short work out of this.  Does it say anything like "fail-safe CMOS loaded" or anything that may indicate that the 3volt battery on the motherboard is dead/dying?  Let mw know what happening so we can get this working for you.

I've often seen problems arise after moving or transporting a PC. The movement will often dislodge something, so check if everything is seated and connected properly.

Recabling the PSU to fix a not turning on PC is usually caused by the following:

1. Bad Caps on the mainboard or the in the PSU. Look for bulging, cracking or leaking capacitors.
2. Spent CMOS battery.
3. Underpowered PSU.

I can't see any any bad caps on the mb or psu interior.
I tried a different cmos battery, no diff.

Here's what's weirder tho --
After swapping the cmos batteries around, it still wasn't starting. But it was beeping once. Finally I figured out the cpu fan had temporarily been unplugged.  So I plugged in in -- and now the PC started starting up again (with the replalcement psu). This was regardless of whether the original battery or the newer batter was in place. AND -- with the replacement PSU, the computer went PAST the post "e" icon and went to windows, several times.  But then it stopped, and now it's only going to the "e" icon. I can't see any rhyme or reason. I've taken out all peripherals, pci cards, swapped memory.

OOoh - -check this out.  It wasn't booting past the "e", with just the P1 and P4 connector plugged in. So I plugged in the hard drive and two cdrom drives. Then it booted all the way (past the "e").  Then I unplugged the cdroms & hard drive. It still booted past the "e". Then I unplugged and replugged teh P1 and P4 cables. NOW it gets stuck on the "e". So I plugged the hard drive, & cdroms BACK IN -- without touching the P1 or P4 connectors. Now it booted to windows.  So i reseated the P1 and P4 connectors -- it still works.

So the consistent thing seems to be -- the higher number of devices are plugged in, the better it works.

Could it be TOO powerful a PSU, even if the ratings on teh wires match?

>>   Could it be TOO powerful a PSU   <<  no - not a chance.
but it never can boot without the disk, since that holds the windows install

Wait, don't confuse the three things --

(1) One is the pc not starting at all, getting no poer
(2) Two is the power coming on, but then it gets stuck on the first pre-POST screen for emachines that says "e". So windows doesn't load regardless.
(3) Three is when the power comes on, and the POST gets past the "e", but windows wont' load becuase the hard drive is unplugged.