Hi there Haqmal,
In case the chkdsk command doesn't help out, you need to use some partition recovery software as it seems that the HDD has lost its partitions. You can check whether this is the case in Disk Management.
Most of the times, this is a result of unsafe ejection of the drive.
After that, I guess you can test the drive with some brand specific testing tool. The results will show you whether there is something wrong with it.
Cheers,
D_Know_WD