It's definitely a voltage problem, or at least a VTT issue. I had the SAME issue as a lot of people where the board would boot fine the fist time, but then fail to boot if restarted (via Windows). For me, I was afraid to go above 1.2 VTT with my E8500 but decided to try it out and see what happened... I set VTT to 1.22 and booted the board, and then restarted via Windows and it actually restarted this time without issue. I then kept lowering VTT until I was satisfied with the VTT value and the stability of my OC. Right now, I've settled for VTT at 1.16 and the board boots and restarts fine.

The funny thing is though, that I never had this problem when I first bought the board... It happened about 2 weeks after, and lasted for a few days. Loading new BIOS's and even a full clear of CMOS with the battery out didn't seem the help. Then one day, just setting VTT above 1.2 got the board acting normal again.