Check if its the lead!
Got caught out recently - my portable hard drive failed 2 months ago so I bought a new one.
The new one "failed" last week - so I bought another new one (I'm in the middle for rolling out 40 netbooks at 2 schools so can't live without it ATM)
Just before I opened the box on the latest one - a little bulb went off in my head - I swapped leads and it was the orig 2 headed - mini USB lead that was faulty - even the orig drive is OK :)
Mr Tesco was a bit shirty about me taking it back (I think he thought I'd magically swapped out the contents of the box without disturbing the packaging and was trying to scam them :) ) but all sorted eventually :)