please try "load optimized defaults" from bios, and then configure pc as you wish. If this does not work...well...seems you got a setting stuck in bios no matter what you change...like I did...I had to force the board a bad overclock to get "CMOS CHECKSUM BAD" before settings I set in bios started to really stick.

I don't know if it's related, but might be. The board reseting to "default" clocks after setting bad settings that would not allow boot was not enough in my case.

Anyway, always best when you first get a board to "LOAD OPTIMIZED DEFAULTS", befoer doing absolutely anything, and doing the same after flashing a fresh bios is a damn good idea too.