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Computer not turning on; trying to figure out the cause

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I shut down, turned off the power supply and unplugged the power cable of my computer so I could move it. Now, with everything plugged back in, the computer doesn't turn on. By turn on, I mean no sound, no moving fan, no display, no nothing except for the LED on my motherboard.

I've removed all extra components to rule them out from being the source of the problem. Here's what I have now:

Motherboard (ASUS A8N-SLI Deluxe)
Power Supply (Sunbeamtech SUNNU550-US)
Graphics Card (XFX GeForce 8800GT)
CPU (AMD 3500+)
512MB RAM x 1 (Corsair CMX 512-3200 C2PT)

All of my HDDs are unplugged for now.

As already mentioned above, the LED on my motherboard does turn on when I flip the power supply switch. I also tested the power supply using a multimeter and have concluded that it's still providing power. (OK, I already knew that before I tested it, since the LED was on.)

I've also cleared the CMOS memory to see if that made any difference, but it didn't.

The power button cable is properly plugged in. Unless there's some invisible damage, that shouldn't be causing the problem.

The attached image is what the computer looks like right now. If you see any problem with how it's set up (i.e. where the cables are connected, etc.), please let me know. It's hard to see in the photo, but the power cable right above the CPU is plugged in. The cable splits there, and the other end is plugged into the motherboard (can be seen right above where blue and red CPU fan cables come out.)

I appreciate any advice, tip, story of past experience, etc. etc. I'm pretty desperate at the moment.

Also, if anyone has information on how much it generally costs to have a computer checked at a store, that would be much appreciated as well.

Thanks for the help!

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Edited by Felius, 06 January 2009 - 02:22 AM.

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I am suspecting a power supply failure as 1st step. You say you measured the voltage?, but what did you measure?

You say no fans are on. Is the fan to the psu on?

Since you measured the voltage, I will assume you know how to use a meter. I will warn you anyways that hazardous voltages are present. Be very careful to not touch 2 pins together or short the test leads.
You need to check all the voltages.
Look at ATX POWER SUPPLY DRAWING for the pinouts on the board coming from the psu.

You can read POWER SUPPLY TESTING, which also gives test points and voltage ranges.

You should have 3.3vdc, +5vdc, -5vdc, +12vdc, -12vdc, and ground to the board.
You should have +5vdc and +12vdc and ground to the drives.
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Thank you for the informative reply! I followed the instructions in one of the links that you provided, and sure enough the power supply wasn't giving out enough power to the motherboard.

I'll try to replace it in the next couple of weeks.

Thanks again for your spot-on help!
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