Well one thing you could do is go to Start > Programs > Accessories > System Tools > System Restore and restore it to an earlier state by following the instructions.
If that fails you could completely reinstall Windows by putting in the Install CD and booting from that instead of the HD. (watch your BIOS screen for a boot option hot key - ie F12 ) then just go through the process of installing XP (I assume its XP you have) which will format the HD to take place.
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I never seen nothin' like you before
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