It might be that you had opened a file on your PC that was contained on a CD / DVD disc, and then removed the disc before closing the file on the PC, in which case the PC may still be trying to access the drive.... or something like that
I assume you have a CD and a DVD drive - try putting discs into both of them, use Windows Explorer to open a file on one of the drives, then close it down again.
Do the same with the other drive.
Remove both discs and close the trays.
Reboot the PC and see if this has solved the problem.
Good Luck
Coconutty