A couple months ago I built my first build and haven't had any problems with it until today.
I mainly built it for gaming and while I was playing WoW today it unexpectedly shut off. Although, it wasn't completely shut off, I could still hear that it was on or in some sort of low power state. I tried pressing the power button and nothing happened, I also tried holding the power button and still nothing happened.
I then unplugged it from the wall and finally it completely shut off.
From there I tried rebooting it and I got to my desktop and the same thing happened, it went to this low power state, but not completely shut off.
I tried rebooting once more, and it didn't even make it to the desktop this time, it went to that low power state while it was starting up.
Also, nothing seemed to be hot except for the HDD and both the CPU and case fan were running fine.
Here are the components -
RAM - CORSAIR XMS3 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model CMX4GX3M2A1600C9
CPU - AMD Phenom II X2 565 Callisto 3.4GHz Socket AM3 80W Dual-Core Desktop Processor HDZ565WFGMBOX
OS - Microsoft Windows 7 Home Premium 64-bit 1-Pack for System Builders - OEM
CD drive - ASUS DRW-24B1ST/BLK/B/AS Black SATA 24X DVD Burner - Bulk - OEM