If the PC has the authenticity/key code sticker but you lack software then beg or borrow a copy! The key code will activate the software. If you put a mega size drive, your BIOS may restrict or "find" half! The other issue and it's a big one is drivers. If don't have the original driver CD, stand by for fun and games! When all is said and done, you may find it cheaper to buy that new or a refurb one!