My computer keeps rebooting...

It first happend 2 weeks ago , I rebooted normally and I got a black screen that gave me 4 options:

Boot in safe mode

Boot in safe mode with network options

Boot windows with the last working settings

Boot windows normally

The first two work fine but the last two dont. it gets to the windows xp loading screen and after that my computer reboots and goes back to the black screen again. When I reformat my computer it works fine but after two reboots or so the same thing happens again and I have to reformat again

this could be because ofa myriad of reasons. first, I would get some compressedair and blow out the dust in your computer. that can cause a heating issue.

If that doesn't work, go into the BIOS and see what the voltages from the PSU are. the PSU may be failing.

If that doesn't work, try running memtest.

if that doens't work try cranking up the voltage on your memory

How do I go into the bios? and how do I run a memtest?

Thanks