locked out while trying to reformat

well, this is a bit of a puzzle. I have an old micron millennia, 800 AMD, 10 gb hd, 512 ram which is a spare computer around the house. it originally had millennium as a os. i reformatted it about a year ago and upgraded to xp home edition. i realize this is a minimum computer for xp, but everything ran fine.
several days ago my son and several of his buddies decided to load a bunch of non-compatible software and hence, the system became buggy. thinking it was no big deal, i started to reformat and therein lies the problem. about 2/3 of the way thru the process, the computer goes blank, black screen non-responsive. i tried reloading millennium, same problem, it's like i'm locked out. we never used any admin passwords.
anyone have any ideas? thanks in advance

 

Hi Rick,

Is it happening while loading Windows or while formatting ?

 

while in the process of reloading windows

 

Is it just after it has finished detecting your video card ?

 

no not really. i have loaded windows all the way to the end, where i have a desktop (then goes black) and at other times the computer goes black about half way through the reload. i though about the video card too so i swapped out monitors, from a little lcd to a crt, but it didn't make a difference.
i've tried this reformat / reload now, eh, maybe a dozen times and the "lock out" (for a lack of a better word) occurrence seems to happen at different stages of reloading windows, whether its xp or millennium
thanks for the help rsinfo

 

Going black or shutting off?
If the AMD processor overheats, and they will as they tend to run a bit hotter than an Intel, your computer's BIOS has a thermal protection that will shut it off.
During hardware detection, the processor could be running at 100% usage, which does heat it up.
A possible solution can be nothing but a can of air, to blow out the dust on the processor heatsink, the vents in the power supply, and any other air vents.