Screen does not turn off

Hello,

OK so basically I open power options and decide to make my laptop's screen turn off after a period of time. But it doesn't. I had the problem all the time now that I think about it, even half a year ago before my windows reinstall. It's just that I didn't thought of it like a big deal. But now my roommate is angry that my laptop's screen illuminating the room at night when i leave it to download something

I tried to look if my screensaver worked. And guess what? I didn't either (I usually don't use it). I've looked around a bit and found out that USB devices cause such problems. So I tried unplugging them all. But the problem persists.
I hope someone knows how to fix this.

Thank you.

P.S. It's a Dell Inspiron 1564 with Windows 7 Home Premium x64.

God...
I feel so stupid now
I rarely ever shut my computer down. I usually just close it (put to sleep).
Thanks. :)