Seemingly random "crash"?

I'm not really sure what I would call my problem so please forgive me if I have labelled it incorrectly. I've had my computer for 3 years now and never had a problem with it, however recently, I've been getting this problem.

If I leave my computer on and alone for too long, (the shortest it has happened with is about 1 hour) when I come back, it will be unresponsive. All programs I had open will be labelled as not responding and attempting to open new programs will not work. This includes any attempt to open the task manager. The only solution I have found is to turn off the computer manually and restart.

I decided to do some tests and discovered that some already-opened programs continue to function. For example, I left a timer running once and when I came back to my computer, it was still counting up, but my previously stated problems persisted.

I can provide any needed information(as I'm sure there is) and run any needed tests. All help is appreciated.
Thanks!

I followed the instructions for a clean boot and ran the file checker. When it was done the result message was:
"Windows Resource Protection did not find any integrity violations."

If it helps, it occurs to me that this could be a problem with the computer attempting to go to sleep. I checked the settings and I have hibernation turned off, though.