Everything is suddenly laggy and some games wont open

Yesterday when I was playing games, everything was fine and was running smoothly but since this morning games has gotten very laggy gaining from 5 to15 fps. I've looked up many tutorials and ask for help but none of them worked. for example yesterday i was playing roblox and nothing was wrong. then when I got back on the next day It would be really laggy and most of the time it wouldnt open, even playing the simplest games would run to 20 - 30 fps when before I had ran 60 fps. I've never came across this problem until now.

:)