Maybe one of you can help me with this. I'm having trouble with EQ2 going from fullscreen to window. Why?
Does this seem to happen when you are typing and press the [Enter] key? If so, your Alt key may be stuck -- Alt+Enter switches between windowed and full screen. Alt+Tab can also cause this. Smack both of your Alt keys a few times and see if the issue goes away. You could also switch out keyboards temporarily to see if that stops the problem. If it changes to windowed when you are not doing anything, it may be another program in the background (maybe an anti-virus program?) trying to get itself or a notification on top of the other windows.
You can clean the keyboard. Blow it out with some canned air. For under $10, you can go to your local big box electronics store and get a keycap puller, that lets you remove the key from the keyboard wso you can clean around it. Or you can get a mini cleaning kit from Amazon with keycap puller, also under $10.