Forbidden Donut

I been having trouble with the power save option for my monitor. I have the option selected for 15 min idle, but it never works. I reselect the option and it only works the first time it is idled 15 min, but the next time it won't work. Anyone have any suggestions to fix this problem.

P.s. I have been shutting off my monitor, but you know, once in a while you forget so it would be helpful in those situations.