Pc is slowing down alot and memory usage in task manager consistently at 80%

Friday and the week before it worked fine, normal speeds. Then Saturday rolled around and ever since I've been having very had slow downs and memory usage is consistently at 80%, havent downloaded anything recently. Have tried using the Memory Dianostic tool, restarts, off and ons, clearing cache wherever I can, deleting games, safe mode, just anything I or google could think of but nothing has changed. Just wanna be able to play my games again