If you have rebooted several times and it still locks up try reinstalling windows-also if you have an emergency boot disk try booting from that and at the c:\ prompt type
dir c:\ then enter key
if you see a blur of files zoom by your harddrive is probably ok-then reinstall windows.
If your computer isn't set up to boot from a floppy you have to enter the bios and tell it to.
When In Doubt-Format and start over