'Oh, now where is it?'

Life For some time now, my little 40 gig hard disk has increasingly become a very cramped place. It's because my entire cd collection is on there, not really leaving much room for anything else. So with my birthday money I decided to invest in a new secondary hard disk. 120 gig. Which is were the modern world rears it's ugly head. Because my little computer is now variously ignoring its existence or else says it's only 8 gig across. I've Asked Mefi about it and they've various suggested that I hack the BIOS or go and buy a whole new computer, both of which sound a bit drastic. Anyone else got any ideas?