If it is not an issue with the bulb being burnt out, it could be the wiring. There could be a problem with the wiring which can also make the bulb not to work. You can have an electrician check it out to see if that could be causing the problem.
It probably a simple fix...unplug the opener, take a flat screw driver and scrape off any residue on the 2 copper contacts inside socket! Then try a new bulb, if that doesn't work, then order a new socket online from the manufacture!