souns like an unhappy driver. whats your windows monitor timer for display set on? you could try turning off hpet in bios . if that dont work. can you just use the timer in windows to let monitors go into standby like normal. if none of this works . roll driver back to the one that worked. most likely you would need to do a clean install of the old driver. if you do that
you see every time you turn a monitor on and off it redetects all monitors , i would say thats rough on windows. but if it worked before roll back to the good driver.