My one and a quarter year old build stopped working.

Well, first off, here's a parts list.

OS____Windows XP Home SP3
CPU___AMD Athlon X2 3800+
HSF___Arctic Cooling Freezer 64 Pro
Mobo__GIGABYTE GA-M61P-S3
GPU___Palit ATi Radeon 4850, 512 MB GDDR3
RAM___A-DATA Extreme, 2GB, DDR2 800
PSU___Corsair TX 650W
HDD___Western Digital Caviar 250GB
Case__Antec Nine Hundred

Now, this build has worked for approximately two months now as I upgraded from a 7600GT to the 4850 around that time along with the 650W PSU (used to be 450W). Anyways, probably starting around three weeks ago, I started having a persistent problem where World of Warcraft would crash at random points in the game, which was usually fixed by going into the game's built-in repair tool and letting that run for a few minutes. After a while I got fed up with having to keep doing this as I thought my XP installation might've cause a virus or something and I decided to wipe the whole thing and start all over just yesterday. After wiping and formatting everything on the machine to a pristine clean slate I started installing everything back to how I like it without any problems. Then I get World of Warcraft all set up, patched and ready only to find that the minute I get into the game world a lot of graphical stuff loads slowly, then it crashes on the spot. At this point I'm very pissed as I was trying to avoid all these crashes in the first place, so I reboot in hopes that it was something temporary. After I got to the Windows welcome screen, there were some graphical glitches in that screen and then the machine reboots again. This time however, it doesn't go past checking the CD/DVD drives in the BIOS. I do a hard reboot to try and get it back to normal and now it won't even show anything at all on the monitor. I've tried several reboots and I can hear all the fans spinning normally inside, but nothing. I've tried plugging the monitor into the integrated graphics and switching to VGA input, but still nothing (though maybe I have to remove the video card first for that to work). To try and test each individual part to find the culprit would be difficult as my PC is the most customizable and most powerful in the house, but also the most unique (just about everything else is a Dell machine at least 3 years old). So, what to do?

TL;DR - PC's not booting anymore and I don't know why. Help.

Well, unfortunately, the CMOS battery is pretty damn hard to remove and I don't have a jumper to use the CMOS clearing pins. I did, however, let a screwdriver rest between them in the hopes it would accomplish the same effect, but doesn't look like it's worked. I've also removed the video card and tried each stick of my RAM individually, but that also did nothing/