Is there a way to fix a polaroid PL126PZ-C external flash? It says its working, but the flash doesn't go off.

If it is external then there is usually a button on it to test the flash. If that fires the flash then you have other problems. If it doesn't then it could be the bulb has gone bad. A photography shop could repair it or you can send it in for repair. Check the OEM website for a list of options.