As to the machine, I see no details so bad advice only. System restore to when it worked.
Just yesterday I started having a new problem, I have been playing on 25-30 fps in LoL. Now every single game my fps has been dropping to 5-10 randomly for a small amount of time and then usually coming back in a minute or so ? When this happens my screen goes black for about 10-30 seconds totally disabling me from playing comes back and I can play at my usual 25-30 fps for the rest of the game usually. I discovered it was overheating, cleaned the pc turned fan speeds up still having the issue however it does not seem to be overheating anymore. I also scanned the pc with malwarebytes/ccleaner. Did not find anything nor think any virus is on the computer. Can't figure out why this suddenly started happening though when it has not been happening for months. Can anyone help me?