PC freezes after returning from idle

I leave my PC on at night. The screen eventually goes to sleep after 1 hour. I usually won't get back on until after work so it's been idle/in sleep for over 12 hours. When I get back on it, for the past week or so, it's been frozen where nothing happens. The display comes back but nothing moves. CTRL+ALT+DLT for Task Manager doesn't even show for a good chunk of time and my PC will beep a couple times. Eventually it will display and my RAM is maxed. It is still displaying the full RAM storage that I originally put in. Normal RAM usage for me is about 10%. I don't get why this is happening all of the sudden after nothing like this initially. I've built this PC like 5 months ago.