Turn off the power to the dimmer rack. Remove the screws from the tabs on the sides of the dimmer in the rack with a screwdriver.
Slide the problem dimmer out far enough to reach the connections on the back. Unplug the three-connector lighting control cord by depressing the metal tab near the cord. There may be two of them: one in, one out. Keep track of which is which by marking them with masking tape tags.
Unplug the cords running to the lights. These will have standard power cord ends, known as Edison plugs. Mark each cord with a masking tape tag, indicating which channel they were plugged into.
Locate the fuse on the back of the unit. These are round, button-type covers. Push in and turn the cover counterclockwise to pop it out. Pull out on the cover to release the fuse. Hold it up to the light. If it appears burnt, or the wire running through the glass cylinder has a gap in it, replace the fuse with a comparable size and amperage.
Twist the cap clockwise to lock it in place. Plug the power cord of the dimmer directly into the wall.
Plug any standard light into the plug-in for the channel you had trouble with. If the light lights, the problem is solved and the dimmer can be reinstalled. If not, replace the dimmer with a similar size and amperage of dimmer.
Reattach the cords in the order and positions you found them in, following the masking tape tags as a guide.
Reinsert the dimmer into the rack and tighten the mounting screws in the tabs on the side to secure it.
Turn on the power to the dimmer rack and test the light circuit. If it lights, you have solved the problem. If not, you will need to troubleshoot the light fixture, lighting board and cabling to restore proper operation.