I've been struggling off and on with this Mac Pro for several days. It worked flawlessly until suddenly it started shutting off at random times. It had a dead PRAM battery, so then I replaced it and it worked perfectly for days, that is until I installed new RAM and a new GPU and the problem started again. It's like being messed with did something to it? Maybe unplugging the power supply caused it to lose some of its charge? What happens is this, it works fine until suddenly theres a click sound and it immediately loses power. Again, it worked for days, and then other times it only worked for minutes or an hour or so.