PC hardware forum: Computer won't turn on

Ok, so here's my story:
Monday night, my PC is working fine. I don't notice any performance loss that would hint at hardware failure. My pc is custom built and has been working for over a year. I use it for extensive 3D animation work and gaming.
THe specs are:
-Pentium 4 Prescott 3E ghz processor HT 1mb L cache
-Motherboard: Intel D865PERL
-Two 512mb sticks of memory
-120 gb HD and 80gb HD
-ATI FireGL x-1 128mb
-DVD burner and a cd burner
-9 case fans
-case: Raidmax http://raidmax.com/product.php?pid=19
-original PSU supplied by Raidmax 420w
but I replaced it with a THermalRock PPV 450w
-SB Live sound card
OS: Windows XP Pro

On tuesday morning, my PC was working fine. I went to school and when I came home, my PC would not start. In one of the front drive bays, I have an LED indicating how much watts is being used. THat LED was lit, and so was the motherboard light.

Backtrack a little:
That tuesday morning I had switched the PSU to OFF ( the switch on the back) because it was making a low, monotone noise; quite annoying. WHen I came home, I switched the PSU back on, but nothing started, not even the fans.

In a frenzy, I began taking out all the parts and at the same time, cleaning the dust from most of the components, I was convinced that the problem has to be the PSU and lo and behold, with a voltmeter, it wouldn't start by itself when I took it out and plugged it into a wall jack. I took a paper clip and put it in the GND and ON location of the 12v connector and used a voltmeter to test each of the volts. Nothing.

Just to make sure my setup for testing the PSU was valid, I found my the original PSU and tested that. It worked fine; showing 3,5, and 12 volts on the voltmeter.

Next, I install the original PSU into the case. But, my PC would not boot up. Reading some advice off the intel website, I took out all the unnecessary components and left the motheroard, RAM, and processors connected. Thinking maybe htere's a shortage or overload somewhere. But nope...

So the problem is that when I plug the 12v connector into the motherboard, no power flows to the fans or any other component. THe motherboard light is on, but nothing else.

I forgot to mention that when I was cleaning out the dust, I also cleaned the CPU and re-applied silicon paste. But before I applied the paste, I had dropped the CPU chip and had some bent needles on the edges. I did my best to straighten them out and made it fit back into the socket. THis could be the problem, but it doesnt make sense because the PC wasn't working even before I started taking everything out. I havent opened the case for months; so no new compnents were added or taken out.

Ok, so when i turn the power switch on in the back of the PSU and take out the 12v connector, I can manually power up a fan. So i'm thinking the problem is with the motherboard or CPU...

but how come? one day it was working and the next it just died. I hadn't ran any intensive applications.

This is frustrating because my college applications are on the HD, along with many other important files. I would transfer my HD to the computer I;m using now, but unfortunately, the PC i'm using now is a couple years old and doesn't have a socket for SATA drives.

Help please? I'm sorry if this post is too long, but I wanted to be as clear as possible.

Thanks in advance.

-kevin