That drive is very obviously having major problems reading - the very fact that you're still using it successfully is rather astonishing imo. The poor drive is probably doing its level best to still read and reallocate/move bad sectors (of which there are probably an increasing number as time goes on) but this is hitting its performance hard. (Needless to say, get everything off there ASAP and then RMA the drive. Running a full diagnostic as already suggested is also a very good idea, but the outcome/diagnosis is already pretty certain.)