Can't detect an external hard disk

hello guys..

Here i have an external WD 320G. It can't detected by my laptop (at My Computer) but when i check at File Manager,it shown that my hard disk work properly. I thought that it maybe because of a virus.

When i remove safely, it have a sound and not inform which drive i'm using it (no Drive(G), Drive (F) etc)

Please help me to solve this problem...I really need the data inside the hard disk..please....=(