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hello all, ive been up the past 5 nights trying to get my new custom built pc to work, after installing windows xp home and pro i am able to play games, load software, and do well anything, until about half hour or an hour the monitor goes blank and nothing will work apart from an annoying beep after bashing the keys, so i turn pc off using power button when pc boots up again i hit rather 1 of 2 errors, with windows xp home i get rather c:\windows\system32\config\system corrupt or file missing, or c:\windows\system32\config\default corrupt or file On windows xp pro i was able to reboot sucessfully once or twice after screen black outs, but now im back to another error, when i boot i get a blue screen UNMOUNTABLE_BOOT_VOLUME , at this very second im following a guide on how to fix this from microsofts website, but i KNOW that once the system is up and running again its only a matter of time before it gets errors again,
also i must note that i cannot get the onboard sound to work after installing its drivers and messing with its settings and activating it in bios i still get no sound, so i have added a pci sound card and sound works on this one. also the errors occured while i was doing the following:
sharing files through network
playing music and opening cd rom drive (sound makes a crackling noise first)
Playing a game.

from formatting and reinstalling windows hopefully you can understand how frustrated and tired i am, and i really hope you guys can help me, heres what i hardware and system info i have to give you thankyou in advance:

AMD ATHLON 2800XP
MERCURY KT400a chipset on board sound ,lan 8x agp slot, ATX
2x 256mb ELIXER DDR 400
QTEC 300WATT PSU AMD AND P4 READY
FLOPPY
GEFORCE FX5500 256MB AGP4X8X
LITE-ON 16 SPEED DVD ROM
LITE-ON CD-RW
80GB EXCELSTOR/HITACHI HDD 7200RPM 2MB CACHE ATA100