in order to troubleshoot the drive you must first remove the metal case around the drive, leaving the tray and laser visible. you will need to turn on your pc with the cd rom drive attached to see if the laser is working and to see if it is moving (the IDE/SATA cable does not have to be attached, only the power cable). be very careful while the comp is on. if the laser moves up and down once the cd tray has been ejected then closed (laser is attempting to read cd), then the gears are not the problem, the laser is. and as GX1_Man previously stated, it will need to be replaced.
BTW do not look directly into the laser...its not good for your eyes.