I'm fairly sure this is a hardware problem, but I don't even know at this point.
A week or so ago, I was showing someone how to build a rig and, because I'm an idiot, I used my own to demonstrate. I basically just ****ed around with it showing cards and RAM and such. The problem is that now, for some reason, the computer just runs... oddly.
It runs slower, but not enough for something to be seriously wrong. For some reason, it takes much longer to boot than it did before I went under the hood and, right after the Windows XP loading screens, the monitor resets itself and then shows the login screen, which it also did not do previously. As far as I can tell, games run the same (but take longer to load). Things also take longer to install. I'm not sure if this happens to anyone else, but it didn't before I opened the computer up: When I run iTunes (or WinAmp), it sometimes slows down little bits (less than a second) of the song if I'm clicking something or anything of that sort. Also, when I run a program, the music will show down. It'll play, but it just comes out in a weird way that makes the song very slow... the only other time I've ever heard it was when I downloaded a program that actually slowed down sounds.
To clarify what I actually did to the computer when I demonstrated:
I reseated the video and sound cards, as well as one stick of RAM (I've checked the RAM and it seems to be fine, so I don't think that's the problem)
I took out one jumper (and made real, real sure that it went back in the same spot, and again, I've checked this. It's not the jumper setting.)
I unplugged a chord that was going from the sound card to the CD/DVD drive because it was tangled in another cable (and made sure it went back correctly)
I removed my slave drive from the bay, but did not unplug any of the chords
... and I did some other things, but I can't exactly remember. I wrote it all down, I'll just have to find it.
Lastly, my specs are this:
ASUS A7N8X Deluxe Motherboard
AMD Athlon 2800+ (2.08 GHz) CPU
ATi Radeon 9600 SE
SoundBlaster Live! (the one from back in the day)
2 256 MB DDR RAM Chips (512 total)
2 120 GB Hard Drives
Belkin Wireless Internet Card (don't know more than that, but it's not the problem)
Windows XP (with latest everything)
I've also got some other cards that don't actually take up PCI slots but take up slots on the back of the case, those being a FireWire port, 2 USB 2.0 slots, and another plug that I'm not exactly sure of its function.
It did some strange things. Once, when the tower was on its side with the side panel off, it simply did not boot. I'm not sure why. Another time, the mouse stopped working. Restarting solved this.
I've tried all sorts of things, and I'm really, really stumped. So far I'm pretty sure that it's not RAM and I'm definitely sure it's not heating.
If anyone has an idea, I'm all ears.