If you're using Windows XP and you get the Servicepack 3 update from Microsoft, make sure you first make a proper backup. If you can make an image with programs like Ghost, before updating. This way you can easlily return to your older system. If installed this service pack twice, with my father in law and my own laptop and both windows installs were not able to boot afterwards. It gave me the message that the OS was missing and didn't boot again. I figure the kernel was f##ked up. After I re-installed the damn computers with a fresh WinXP, I could install service pack 3 without any problems. I was glad I did a backup before, so I could put my files back...