The term is reformat. Like Marforce said, insert your OS CD and do a format then fresh install but make sure you insert it in bootup. But, I don't think its neccesary to reformat unless it really is hopeless to recover.
Usually, you can wipe out a virus with your anti-virus software (that's if the virus didn't cripple that first...); a reformat is if the virus is bad and nothing can help it.
the virus is bad all of Av won't pick it up and it shut down my disc drive that it won't register my drive as being there