If you go into MS Dos then you can type in Format C: (or whatever drive, no \) it will ask you some obvious stuff and say you will loose everything. Once its done you can put in the Windows 98 CD and it will install. Then you get a clean install.
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.