Eeekkk.
More info please.
What is your hardware? Your software? Your OS?
When did this start happening? Did you recently install any new hardware/software?
Adder.
Asus p4p800 Delux
Intel P 2.8 g
Xpet 128 ati rage 128 gl (pci)
Win. Xp pro. Sp2
DVDR Plextor px708a
200 g Serial ata HD
13 g IDE HD Primary
kingston ddr 512 400
Optiquest v775-2 on Xpert 128
BINGO! Although your problem may be because of something else, SP2, IMHO opinion, is nothing more than an enhanced firewall/popup blocker. There is absolutely no benefit in installing it and a world of hurt for numerous peeps who have installed it.
The worst thing about Windows Update, is that if you want to do a Format C: and install SP1 and all of the SP1 updates, you can no longer do it on Microsoft's site. There is a site, elsewhere, that has SP1 and all of the updates. If someone wants it, I will post it here, if that is not against the rules of posting.