I have aDell dimension 2400 with windows xp in it and I want to restart the entire system, I have already backed up I want to keep now I just want to wipe everything out please help me

Just put the windows disk in and reboot, it will ask if you want to load from cd say yes, from there the menus are prety user friendly, select re-install windows

Reboot means to power off and back on the system. Restart means something similar. What I think you want is to restore your system to the wayt it came from the factory. If that's what you mean you need to boot to your Recovery CDs.

If that's not what you mean, please clarify.

Do you mean you want to re-format your computer altogether, that is wipe off all its content off the hardrive and re install the discs. If so take a look at this site, it should help:- On TV - The Gadget Show...