Four days ago I was on my computer (its a dyi - about mobo, hsf, and psu about 5 years old, other components are newer) when it suddenly shut down. I then pushed the power button and nothing happened. I unplugged it, tried to turn it on and again nothing happened. I then tried a third time and it booted up fine. CPUID show temps are all fine. It's never done this before, and so far if hasn't done it again. Any ideas why it happened?