I just solved my problem with my monitor not going to sleep. firstly i would recommend doing ALL the other checks that r recommended here,ie making sure that the power option is not set 2 NEVER , ect,ect.
so this what i did #1 i set the power option to 1min. ( the min.) so as i checked dif things i didnt have 2 wait a long time(i also used a stopwatch)
#2 i unplugged diff peripherals ,1 @a time, waited the 1 min 2 see if my monitor would go 2 sleep . I use a controller 4 some of my games, so when i unplugged the controller my monitor went 2 sleep after 1 min.
I know that most of u dont use a controller but its the testing the diff peripherals that might solve your problem .The use of a controller had also caused a problem with my Steam launch, causing it to take up to 2.5 min to launch.I dont know what the controller had to do with the monitor not going 2 sleep but its now been 3 days with no problems.
I hope this helps some of u with this issue.
Aztec.