The other day I was on my computer when I wasn't supposed to and when my mom got home I shut it off normally and properly. Then the next time I tried to start it, the computer just keeps refreshing itself. Once it gets to the Windows loading screen it completly restarts and wont load. I tried unplugging it and letting it sit over night and nothing helped.
Virus maybe? Try booting it into safe mode It could be hardware failure, though I doubt that any piece of hardware can overheat that fast.
Happened to me, I had another keyboard plugged in, it the F1 key, make sure its not screwy, and make sure you only have one keyboard plugged in!
Constant reboot can be either hardware or software...no likely from overheating though. Hardware problems would be like bad memory past the amount required to POST, unstable speeds; like if you overclock, bad spot on the HDD causing a software error...etc. More then likely it's software based and you crapped a driver or some other required system file. First try safemode as suggested. Actually use another computer, download knoppix, backup all data and just do a clean install much easier.
you can try reinstalling windows (you wont lose your files if you do it right) which should fix it. but that depends on how far it gets before restarting.
take a look at your BIOS as well and "restore to defaults" maybe something got messed up in the booting process