Help.

Well I was running my computer at 200x11.5 with 1.85 vcore,Ran it that way for 5 months.It passed prime for 16 hours and it passed memtest.Temp was 41c idle.I thought everything was smooth,but the other day I had it on and I stepped outside for a while and I came back in and had nothing on the screen.My fans were turning and everything but a black screen. Well I held down the power button and shut it down.Powered back on and it said "system failed memory test"and wouldn't post.I powered back off and back on ,then went into bios and lowered it to 200x11 and it posts now.It will power up everytime,so why you think it won't at 200x11.5?Is it the memory you guys think?The strange thing is that memtest will still run errorless.I use 6,2,2,2 timings.But at 200x11.5 it wont power up.It always says"system failed memory test"I have Corsair comeing Wednesday.Maybe this will fix it.

I dont have a surefire explanation for you, but Ive had probably 3 Asus boards over the years, and they are very finicky. My P4PE did just about the same things you speak of