2 TB Unallocated, empty 500 GB seagate hard disk

[rkhemarun]

Dear all,
My 500 Gb seagate external hard disk is not getting detected by Win Xp. It is detecting as USB mass storage but not displaying in My computer. In Computer management too it is not displayed. It is showing 2 TB, unallocated empty space in laptop. There is a lot of data regarding my R & D. Please help me to fix this problem.

Thanks