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