Seagate Freeagent Go-Flex 1TB HD Error

Hello,
My Seagate Freeagent Go-Flex 1TB HD has an error.I took it to my friend office and borrowed him for a while, after a few hours later, I took it back and when I plugged it to my Desktop PC(Windows XP), asked me to reformat my drive.So, I was freaked out and brought it home and test it with my 3d TV and everything was fine.I can still watch my movies perfectly which was stored in the hard-drive.So, the problem is only occur when I try to use it with my computer.The Last time I try to use it on my PC, It didn't showed up under My computer Folder, but I can still see it in Disk Management and a drive letter is assign.So, can anyone please help me for this situation.