A gremlin in the mix

Alright. I've got this problem with my custom made computer, that's got a few years under its belt.

Upon system booting up (which it won't), it wont leave bios. It runs all of its checks and then when its reading the MBR on my drive, it sort of halts, and a few random characters/letters on the bios post screen change color from the normal white to something weird, which led me to believe that possibly was wrong with my video card, an ATI radeon 9800, because it gave me a graphical response with the few bios letters changing colors. Originally I thought it was my harddrive and it was just messed up somehow, so i put a freshly installed OS on a newer drive right out of install off of a system that works in, and it didnt change anything. So i thought, maybe my video cards gotten messed up and it cant switch into higher end levels of functionality (or something along those lines, kind of the way it acts if you dont have the power running into the card and its getting its only power from the board agp slot connection).

But, I throw the video card in a different system and it works flawlessly, so its not that. I figure, it must be an issue with the motherboard, seeing as how its kind of old, and ive given it a little bit of a beating over the last few years with upgrades and cramming memory in and out of it when benching parts for other computers. So i buy another, even better board, since I was pretty sure its where my issue was, and the system is still behaving the exact same way, not wanting to leave dos and a few of the characters onscreen change color. Shortly after, doing a little bit of parts swapping, the system decides not to boot at all, and i smell this weird odor coming out, and can't turn on even to bios anymore.

So, any ideas? Considering its got a fresh harddrive with a fresh OS install, i dont think its that. The motherboard is brand new, so i dont think its that. The video card worked great when i benched it in another system. All thats left, I think, would be the power supply, but Ive never had one die on me before so I'm not sure how it would behave.

The power supply in question is about 3 years old, and has run a ton of hours through it, since i used the box as a server for a time and like most people leave it on around the clock. Is it plausible that the power supply was dying and wasnt generating enough power for the graphics card to flip over to the higherend level of graphics for the boot screen, and then finally died? Or is the issue somewhere else?

Any help anyone might have would be greatly appreciated