Sleep mode question

[thehellwas that]

hi i built a pc a few months ago and had no real problems with anything till now. for some reason my pc wont go into sleep mode. i havent added anything to it or done anything diffent it just stopped doin it. i have it set so after an hour it goes into sleep but it just stays on my screen shuts off but it stays running. no clue wats goin on there ive changed the times and i can manually put it to sleep but it wont do it automatically. it worked then nope haha
thx for the help

 

[Ultimate_Destructo]

what is the operating system?