Something on the drive is likely corrupt or broken. The problem is that any write activity to the drive will worsen corruption, and if there is a physical problem any activity on the drive at all can worsen it.
The usual response here is to try to either
Repair the drive's MBR, partition table, and other structures with some sort of partition editing tool
Use one of many tools like Clonezilla that will scan the drive sector-by-sector and try to reconstruct files and directory structures from whatever it finds.
If you look for similar cases in these forums you will find reams of advice on the subject. Good luck.
I m getting message when i plug the usb hard disk drive it giving message need to format i cnt format the drive becoase there is lot of data in the drive kindly help me in this regard.
This sometimes happens if you plug it into a different USB port than before. If this is the case, safely remove the drive, go into Device Manager, right click on 'Universal Serial Bus controllers' and select 'Scan for hardware changes'. This updates the USB hardware information. Then you can reconnect the drive and the system will load the drivers and the assigned drive letter should be the same.
This works for me with a 1TB USB drive with four partitions on it that map to drives D:, K:, L:, and N: If I change its USB port and rescan the USB hardware, the partitions stay correctly mapped to those drive letters.