The capacitor that charges up can weaken, in time, but usually the zenon bulb will either work or it won't. You may be having a timing problem with the flash and the shutter. Also, some cameras have trouble focusing in dark scenes, also, and that may be happening in your case, in addition to the problem you're having. You can try other scene settings, to see if the camera operates better in those modes. Otherwise, you will have to have a repair shop check it out. Make sure you get an estimate before you do, since repair can be expensive. Wish there was an easy answer and fix to this problem, but there just isn't.
Answers & Comments
The capacitor that charges up can weaken, in time, but usually the zenon bulb will either work or it won't. You may be having a timing problem with the flash and the shutter. Also, some cameras have trouble focusing in dark scenes, also, and that may be happening in your case, in addition to the problem you're having. You can try other scene settings, to see if the camera operates better in those modes. Otherwise, you will have to have a repair shop check it out. Make sure you get an estimate before you do, since repair can be expensive. Wish there was an easy answer and fix to this problem, but there just isn't.