Power Management is generally referring to STandby, Hibernation, or power on or off issues. I find that overheating can be a bigger possibility.. Start by removing the case cover and blow out all the dust and junk from around the processor, heat sink, all the fans, and everywhere else. Check for bulging or leaking capacitors on the motherboard. Try running the machine without the cover on and a house fan pointed at it.. If that fixes it, then you've found the problem.

On the other hand, a faulty power supply can cause such issues as well. Replacing the usual underpowered supply unit with one of more watts could cure the issue as well.

Hope this helps.