macbook pro sleep problems/ won't come back up

Lately, about once a day or so, I'll close my mac without shutting it down, and I'll notice that it isn't going into sleep mode properly. The white light stays on instead of slowly flashing on and off. when I open it back up, the screen is black and nothing I do can get it to come back on...I have to force restart. I've been paying attention to the activity monitor, but the problem is that when this happens, I can't see the screen, so I can't tell what's going on. This is getting really annoying; help would be appreciated!