display – Black screen with cursor out of nowhere while using PC, can’t do anything in it

I’ve looked online but they all address the problem only on start up or after login. This doesn’t happen at either of those times, instead it happens around an hour later while I’m using it. The screen just goes black and all that’s left is the cursor. CTRL+ALT+DEL doesn’t work, CTRL+SHIFT+ESC doesn’t work either, nothing works.

Sometimes the display turns off and the monitor says “cable not connected” when the cable IS connected instead.