Windows 7: Disappearing Drive

Hello All,
I've had this problem for awhile, but here goes.
I have an HP computer its a few years old. I have two
optical drives on it one internal and one USB external.
For some reason the external drive sometimes disappears
from the computer. I can't find it anywhere then a few days
later it pops back up. I have tried replacing the cables and
checked to power and still the problem continues. I also tried
reinstalled the system and sometimes it works.
If anyone has any help it would be appreciated.

RalphG.

Is the external drive powered from the mains?

Its powered directly to the power strip.