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PC will now power up

Deerek11 asked
Medium Priority
Last Modified: 2012-05-12
I got an pc that a usb flash drive was remove from the system and it locked up after that turn it off and then it would not power back up, the little green light on the back of the power supply comes on when I attach a power cable but when I hit the power button nothing happens also the little green lite on the power supply flashing a bit when the power button is hit ... would you say this board is fried? .. would u just replace the board or the cpu could be bad also?
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Hi Deerek11

What make and Model is the PC in question?
Maybe unplug the power cable for about 30 to 45 seconds. Plug it back in and try the power button again.

Any time you are checking start up issues, you need to strip it and go to basics.  By strip it I mean remove everything but processor.
If you unplug ALL drives, remove the ram sticks and remove all non-essential boards, like extra video cards, sound cards, modems, nics and anything but the primary video, if you have a video card and also have onboard video, remove the video card.
 Now try to boot the system,  if it's posting, it will give you a long beep indicating that the ram is missing.... this is good...
   Next you power off and put the ram back in and try again... if it posts past the ram you will get a message that it cant find the hard drive.... again, you are making progress.... you want to see if something that is plugged in is causing no boot...
   If however, the system does nothing when you try to boot it stripped, then the only other thing to do is test the psu... you can do this with a tester, or a multimeter.   If this is the case, and you need the wiring diag to test the psu, let me know and I will get it for you.


The mode is Comaq presario SR2150NX  

I have remove everything attach to the board and the memory and attached power and still nothing ...  
Ok, you will need to test the psu to make sure it isn't the culprit.   If you dont' have a psu tester, or another psu that you can substitute, you can do this with a multimeter.  
    You will need to put the psu under load to test.  so plug the psu into the hard drive, this will cause the hard drive to spin up and create enough load on the psu for a good test.  
   Next, remove the psu plug from the mainboard, this is the long white plug with either 20 or 24 pins that goes from psu to mainboard.  
   having that removed, take a metal paperclip and bend it in a horseshoe shape.  You are going to activate the psu by shorting out the green and black wires.  This is not dangerous and if the psu is working this will cause it to kick on, don't be alarmed.  You need to take one end of the paperclip and put it in the hole where the green wire is, and the other end where one of the black wires is, (doesn't matter which black wire).  If the psu comes on, proceed with the next step.  If it doesn't, you have found a bad psu.  replace and see if the board boots.  
   Next step, you will set your multimeter to dc voltage, 12 or 20 volts whichever setting you have.  You are now going to test each of the below colors on the plug to see if they are in range, if they are above or below the range listed, then you have a bad psu and it needs to be replaced.  It is possible that both the board and the psu are bad, but psu is the place to start.    You will need to leave the paperclip inserted and the psu powered on for this test.  Insert the black probe from your mulitimeter into any of the black wires on the plug, then use the red probe to determine the voltages listed below.
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)

     If all of these voltages are within range, your psu can be called good, and then it will be the mainboard.  I'm not sure the age of the system, but if it's within 3 years, I usually say look for a board... if it's older than that, I typically recommend replacing the system.
   Just in case someone who really wants to get technical chimes in, yes, it could also be the cpu, but this is so unlikely that I would offer a wager against it.  I've been doing this for 17+ years and have yet to find a cpu bad that kept a system from booting.  You have eliminated all other possibles by stripping the system. It's either the mainboard or the psu or both at this point.
   Let me know if I can be of further assistance.
Distinguished Expert 2019

is this power supply Bestec?  i just had one with a flickering green light on the back
it WAS BAD  -nearly all capacitors inside were bulging and leaking

note - sometimes they still power on a couple of times- but don't rely on that

Curiousity has me wondering.... what was the final outcome?

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