how do i clean my hard drive and start over again?

Answer 1

the easiest way is to get a copy of the operating system that you want to install. Start your machine from the disc and, assuming you're using XP or above, you'll be given the option of a fresh installation while wiping your hard drive. really straightforward. good luck.

Answer 2

You can format your Harddrive if you have a copy of your Operating System to reinstall once you are done. Or you can buy yourself a new harddrive (you will still need an OS). Harddrives are quite cheap nowdays and you can get a 300 gig harddrive for about 100 dollars.