download the diagnostic program from the manufacturer to do a low level format. it will kiss off any info on the hd.
If you are talking about your main drive (c:\) with your operating system on then you could try a repair... If it is WinXP then pop in the disc and boot from it on startup, the first screen has press R for Recovery Console DONT press R at this time but press Enter and let the setup detect your operating system, now press R for repair, XP setup will now re-write all the main files and hopefully make it boot again.... Hope that helps : ) If not do what ddp said...
