Disappearing HDD?

What the title says, got a new HDD the other week there (750GB Seagate, forget the serial code) and slapped it on the computer. Went and formatted it and it runs fine on my PC, except earlier today (a week after installation) the thing has mysteriously disappeared from My Computer. Its a secondary drive (used for music, games and film storage) but I dont get why it would disappear. I rebooted and there it was back again. Just there now before shutting it down I noticed that it had once again disappeared from My Computer. BTW checked it in BIOS; it IS listed/detected under Bootable Drives so I really am stumped =/ Any ideas lads? PS - the primary system HDD (200GB Maxtor) has had no problems so far.

I suggest checking the leads, make sure you take the proper safety precautions, but make sure they are securely connected, maybe try another cable if you have one spare, see if that helps.