What no details, please provide.
WAG, there maybe a video or USB issue at fault. You mentioned "level" so i guess that some game. if you game alot, you're getting whatever is starting to falter to cause a freeze or hang. I suggest it maybe the video.
On the other hand, if you have alot of USB devices attached, they maybe holding down the PS. Even, if they don't get used, they are polled now and then, then they suppose to idle. Upon waking them-up they cause a slight freeze or apparent inaction but it's really trying to recover. The more USB devices attached, the longer it takes. If you have a power hungry device, it may need more time.
You may want to check your "system setting" and review them for your OS being used. understand what it to hibernate or sleep or what it does overall. here's a link for Win7:
-OR- check the mouse setting too. Plus check what is running in the backgrd. of pgms., if you got too much going on or tasking the ram, its just too much to maintain it all.
This problem has a few angles I guess so I'll lay them all out here.
First if my computer idles I have difficulty getting it going again. To get it going again I have to turn the monitor off and on then move the mouse around (usually repeating this 5 or so times before it hold in non idle mode).
Second sometimes it briefly goes idle when i start when i start a video game or video or if my video game is loading a level or something. I say briefly idle because it can be fixed with a monitor off then on.
Third, I was recently playing a game that requires a controller and the controller kept disconnecting and reconnecting. Each time this happened my computer would go idle similar to the second problem.
I think that's it but i might be forgetting something. Let me know what you think!