External drive not consistent anymore..

running the 5oogig premium es edition mybook, all was going well, but recently it has been dropping out after loading up, I dont have the clicking noises ive seen you guys mentioning, and it spins up, and lights behave as usual.. at moment i'm trying to update drivers, and now cant find it at all!, coming up as a unrecognized usb device.. when it was working well, it would turn on and off with the pc, now it wont do that, and i cant find anything through power options to change this, (running vista sp1) why does it seem buttoin manager has been taken over by drive manager, and is this related to my problems???.. Thanks in advance..