As you can see, dell's don't upgrade easily. Your power supply may or may not be adequate, but before you spend any more, try your original cpu and see if it still works. If it does, I suggest you leave it alone. You may have the board going out or simply need to reset the bios, which can be done by removing the motherboard battery for one minute with the power supply unplugged, then reinstall. The board is fairly old; any board or power supply over four years old can fail at any time. I find parts sometimes on craigslist but you have to negotiate a decent price; some parts are priced too high. Good luck.