Re: Help please, computer has started locking up
You're overclocking - general rule #1 when it comes to overclocking - drop your clocks and timings back to base settings to isolate issues with the system - if the issues persist, dig deeper.
Heat is a possibility, but while you list the specs for your system, you haven't mentioned which power supply it is. I don't trust software to do true and accurate diagnosing of a power supply - they can look at certain metrics sure, but for the most part, you need to test the unit yourself, physically (and manually) with the right equipment to get a real idea of what's going on in there.
Since you've already run MemTest, you've got that base covered at least.