Format harddisk without using os CD?

Do One Thing. Try Any Freeware Software like Dban Or Killdisk. You Have To Create A Bootable CD Out Of It And Run The CD On Your PC. If The Computer Does Not Display "Boot From CD Or DVD" At Boot, Then Go In The Advanced BiOS Features In Your BiOS And Change The Boot Priority Setting As :-

1. Floppy / CD Or DVD

2. CD Or DVD / Floppy

3. Hard Disk

Hope This Helps.