Yeah man, it would help to have some information as to exactly what kind of mac you have (iBook, PowerBook, etc.) and what system software you're using. Can you find the "disk utility" in your utilities folder (in the applications folder)? If so, try running it and fixing permissions... If you don't have any kind of bootable system disk, then you're gonna have a hard time zeroing out & reinstalling anything. You might be able to buy one on ebay.