WD My Passport detected but not assigned a drive letter

I have a WD My Passport external drive which used to work fine on my Win7 x64 box until recently. Since the past few days, windows would not detect my external drive. However, Storage under disk management lists my external drive(which means windows can see my drive) but without a drive letter. I am not able to assign a drive letter(the option is grayed out). I installed EASUS Partition Manager which allows me to assign a drive letter, but fails to do so when I apply to save changes. What do i do to assign a drive letter to the drive or make windows to detect it as of old? The external drive works well on Win7 x32(dual boot, same system) and win7 x64 on another box. Update: cant comment from Opera Mini 6 @zeke the drive works absolutely fine on other Win7 boxes and on the dual boot win7 on the same system.

Solution 1:

I had already tried uninstalling the WD drive and removing the drivers from Device Manager, however, reattaching the drive resulted in the drive being installed but not displayed. Then I noticed an entry in Device Manager>Storage Devices> called "Unknown Device". The device did not have an exclamatory sign or cross sign to indicate problems with the device. I uninstalled it, uninstalled the WD SES entry from Device Manager and rescanned for hardware changes. Windows detected my drive and Autoplay popped up prompting to play videos or open folder to view the drive.

The Device Manager does not have the Unknown device listed now.

I also installed USBDLM, which showed a balloon tip telling me that the drive had been assigned the letter J. I don't think using USBDLM was necessary in this case, but I haven't verified otherwise.