As everyone says, its most likely in your 5 volt circuit. Its always mentally satisfying to know the exact cause of the problem, but sometimes the shotgun approach works well too. Replace: voltage regulator, BR,both Caps ( the big one and the little one), Then do the wiring mods on the back of the board in case you have a bad trace.
The cost of the parts are cheap. Doing them all at once is not that much more time.