PROBLEM WITH WD 500GB EXTERNAL HARD-DRIVE

Hello,
before a couple days something weird happing to my harddrive ... i had my HD for 2 years ago and everything going fine a couple days i connected the HD to move some data on it and unfortunately i used CUT & PASTE method not COPY & PASTE .. but it doesnt complete transferring data and it stopped or freezed i cant remember so i restart and back cant read at all ... i really had 2 partitions on it divided to 250GB each .. so i kept it for other day when i connected partitions comes again 1 working great but the other one who was moving the data has failed always ... i dont know what happens .. i used to check HD with Western Digital Software it tells me alot of BAD SECTOR .. but sometimes it works i moved some date from it then it FREEZED again ... while i am trying to resolve the problem by connecting everyday for less min's and freezed ,now the PARTITION DISAPPEARED AT ALL .. DAMN did i lose the data .. i just wanna know what is the problem exactly .. i am using windows VISTA and i connected to onther PC have XP same problem .. do u think its electric voltage problem coz it freezed but when i am using the other partition it works like a charm .. i really need the to recover the date from onther partition .. even so when i boot windows connecting the HD it freezed till i remove the USB .. if any one has face this problem or have any clue please help me ..... sorry for bad english .. and thanks in advanced ...