OU, I recently had a problem with spontaneous shutdowns, which eventually morphed into something more sinister and appeared to be a mobo problem. I also have an ASUS mobo. Here's what solved the problem for me: Take out the CMOS battery, move the jumper cap on the three prongs below where the battery sits to the right 2 prongs for 10 secs, then replace on the left 2 prongs and reinsert the CMOS. This solved things for my ASUS mobo. Don't know if it would help your problem, but may be worth a try. . .
Newly