|Do you have EVERYTHING from the hard drive stored on CD, DVD, or other hard drive?|
Do you have the restore discs for the machine?
Formatting the drive is not a problem; it's getting the drivers and windows back on and working that is the challenge. The restore disc for the machine will format and install at the same time. Just boot that disc and away you go.
If you want more information, we need make and model of your system.