check you powersupply, chances are that it is the one that is actually the culprit instead of the rest of your system. power supplies tend to be the first to go before mainboards unless you are overclocking. processors rarely ever die under normal use and your description doesn't fit a bad memory chip. this all assumes that you haven't been playing around with parts inside prior your system failures besides vacuming dust off of air ducts.

makes sense that after it had sat overnight, it ran longer than it did when you were trying to get it back up after a system shutdown.

at this point, I am willing to bet ingame gold its a powersupply issue,