|Sounds like you have a connector issue. You may need a new external enclosure.|
Saving ONLY one copy of any personal data is just asking to be hurt. There are so many ways for you to lose that irreplaceable data. You should keep at least two copies of any files you want to retain. If the data is very important you should make even more than two and keep one off site.
Burn the data to DVDR and then you can duplicate the disks as needed.
Going back to you immediate issue. The file system may have become corrupted by improper disconnection. Look in Windows Disk Management to see if the drive shows there. If it does, post any information you see for that drive.