My best guess at this point is reflash should be your first attempt, since more mundane stuff seems to not work. If the reflash doesn't work (try a couple, if you want to first try one with a backup. If restoring programs from backup results in the same problem, reflash and see if not restoring makes it work. Then you can add programs back on one at a time to see if any cause this problem), it may be a faulty battery. If getting a new battery doesn't help, then perhaps taking it to Nokia will be the only option, since at that point it's probably a hardware issue.