When looking for attached hard drives, USB flash drives or CD and DVD drives using Windows Explorer, you may notice that some drives are not seen in Windows Explorer or the drive may disappear after a short time or when Windows resumes from Sleep or Hibernation.

This can be caused by any of the following:
  1. Your drive does not have a drive letter assigned to it in Disk Management
  2. The drive may be disabled or offline
  3. Your USB driver may be corrupted
  4. Corrupted registry keys may be causing issues with connecting toyour CD or DVD drive.

Run Hardware and Device troubleshooter and see if it helps you.

If not, KB330140 may help you.