Just started having problems with this. I've got an EVGA 780i SLI using an Intel QX6800 CPU, OCZ Reaper DDR2-1066 memory, 2 EVGA GTX 465 video cards, etc. Yesterday, I encountered an odd issue where both my keyboard and mouse (both USB) suddenly failed and had to be re-plugged to get them to work. Everything seemed fine after that, I kept using the computer all day and it worked fine, then shut it off at night.
 
Next day, today. I go to boot it up. And nothing. I was using the EVGA splash screen and it would hang right there. So I reset the CMOS jumper and pulled the 2nd GPU. Now it'll POST, and it gets past the memory test, it'll hang right when it says "E64T CPU supported" or whatever, and the POST code it halts on is 52.
 
First thing I did was swap out memory, since code 52 is a memory issue. I swapped it out with 2 other sets, trying different DIMMS, trying just 1 stick in different slots. Memory that I know for a fact works. Nothing, still does the same thing. I've read up on this and it could be a USB issue, so of course I unplugged all the peripherals. Nothing, no change.
 
Right now, the computer is sitting open with everything unplugged and the CMOS jumper and battery removed. I'm going to try to let it clear, then go for a barebones boot. If that doesn't work...
 
To me, it sounds like the motherboard is bad . My USB keyboard and mouse crashing yesterday seems to point towards the USB ports failing on the mobo? Can I get some help here, does it sound like I'm on the right track?