Virus infected PC

An HP PC, running Win ME, seems to be infected with a virus, it will not start Windows. I’ve tried to reinstall Win 95, Win 98 and Win XP and it appears to be installing the software but when it stars running Windows, it freezes. I’ve reformatted the hard drive twice.

Can a virus be removed by reformatting?

How can a virus be removed without being able to start Windows?

Thanks!