You will need to boot the PC into safemode, its slightly different with every PC, but you either hold down the " DELETE " key or one of the function keys, normally the " F5 or F8 " key while you turn on the PC. Keep pressing it until you hear a beep noise and the PC starts up in safe mode. From here you should be able to use your windows boot discs.
This should resolve your problem, but If you cant get your PC into safe mode, then there are products on the market which can retreive hidden / deleted data. You say you have access to another PC, search the download section under hard disk, there are several recovery programs ( EASY RECOVERY )might help you.
Let us know how you get on.