For some reason my computer just reboots itself on me while I am using it, and it is starting to do it alot. I'm not sure what is wrong with it. I tried a few things, but nothign seems to help.
If something like this happen to any of you can ya drop me a line

Usually the power supply. Could be overheating or memory too.

I've had systems do that before. All of Sanchek's suggestions could be it, but for me it has usually been overheating issues. Try running it with the case open if this can be done safely (IE, no cats wandering into it). If this resolves it, look into some better cooling / ventilation. Then again, if the room you have your computer in is excessively warm, this might not help.

It could be the power supply in 2 cases:

1) your powersupply is going faulty... hard to troubleshoot.
2) you just added something to the system (new vid card, another burner, etc) and it is causing your system to pull more power than your PS can supply.

friends comp was doing stuff like that a while back , motherboard had a built in temp auto shut down feature on it. he had to remove a little black jumper switch thingy that was on the MB to disable it (looks like the thing they have on disk drives to pick slave or master)

/sarcasim on yup i know alot about computer repair,put gas in it, if it dont start get a bigger hammer then call dave :D /sarcasim off

If your computer is shutting down because it's overheating, I probably wouldn't disable that feature. That feature is probably stopping your valueable components from getting completely fried. Address the issue, dont disable the protection measure :(

What kind of system are you running?

I had an older Pentium 4 system with an Intel motherboard, which used to randomly reboot on me as well. After checking a couple of things, the culprit turned out to be bad RAM on my end. After I replaced the RAM, the thing was a rock for stability. You can verify your RAM by running MemTest86 overnight. Then again, these random reboots were also a symptom of Windows automatically rebooting itself after a blue screen.

If you're not getting blue screens, then it's probably related to heat or power, as mentioned.

Check power supply as well.

I know that there was an issue for awhile with the Antec NeoHE PS's

What are you doing when it reboots? If you're running memory intensive stuff, do a search for some memory testers. Memory and heat are both likely, and easy to fix. A PSU is a little harder to troubleshoot.

What sort of motherboard? Many of the modern manufacturers have a temp probe on the board, you might be able to download a utility to let you see how hot your box is getting.