
mmm, that's an odd one.
Never heard of software causing drives to disappear, I think it's unlikely to be a software glitch given you've rolled back your system to a time when I assume your drive was being recognised.
If it's not even appearing in Device Manager then as far as your computer is concerned it simply isn't there anymore.
Therefore I fancy we're looking at a hardware problem.
Easiest fix - take your cover off and make sure everything is as it should be - e.g. power connector to the drive (must be okay if the eject button works), data ribbon connectors - in the back of the drive and on the motherboard - give up a push to ensure nothings come loose.
Failing that - perhaps somethings gone on the drive (or worse, the board).

I tend to look on the optimistic side with these things, work from the simplest solution and go progressively toward worse case scenario.
Try the drive in another computer - that'll tell you if the problem is with the unit or your computer.
Kazaa - arrgh! Stay away from peer to peer software hazards is my advice. Nothing like having an open invitation into your system - I've heard lots of scare stories about Kazaa, dunno if it's urban myth or factual, but I don't go near such stuff.
DaveB - LinuxWannabee