Here's the issue. 95% of the time when I turn my self-made HTPC it will not boot. It POSTs fine (single beep) but then proceeds to a black screen with a flashing cursor. Its not an MBR issue, it will not boot from a USB or CD consistently (has a few times). I have run memtest+ a couple of times (when it decides to boot off a usb stick) with no apparent errors. After changing BIOS settings, I was able to randomly get it to boot once. Then, when shutdown, it would not start again.
Here is what I have done:
Changed PSU, motherboard, and RAM- no change with any.
Odd (maybe related) issues: the motherboard will occasionally fail to power the USB fully (to the point that the keyboard will not work in the BIOS). This happens with both motherboards (ASRock a75m-itx).