Hello everyone got a small problem with xp pro s2 maybe?

Ok I built this pc about year and half ago and loaded it with Windows xp pro s1. The other day the lady gives me a call and says aol want connect it goes so far and stops. When I get
there the cpu goes to 100% when I try and load up aol wow! I try this and that and nothing is working so im think that the hard drive is dying and try a format to see if that will fix it big
mistake! I don't have pro service pack 1 anymore all I have is Service pack 2 . Anyway when I try to load xp back quick format want work It all ways says check your hardware device
make sure it connected correctly and so on, go back and select a different format. When I go back and try again I get the blue screen of death. So I restart and try load normal it loads
and im happy until I try and click on windows update the blue screen o death again and restarts. I load back up and decide to try and change screen res damn blue screen again. this time
it tries to load up and just keeps restarting. long story short I try to format again and it want take any format from xp pro. I try a new everything Ram ,Powersupply,video card,everything
short of mother board same result. So I took the Hard drive just to test plug it into my back up pc and start loading windows it works fine takes Quick format and works like a champ. Its
not the hard drive. Well at this point the only other OS I have is 98 or 95 so I load 98 to it and it runs like a champ grrrrr. I have been scratching my head for three days now maybe one
of you can help me here for im stuck and don't know what ells to try.