@glittermeowed How did you start the game? If you just hit the big arrow at the main screen, you may have just started a new game if it went straight to CAS. Use the load option and see if the game you were playing comes up in the list of saves and select it there. And it should come up.
I had this happen too when I got new computer a while back and moved my saves folder from my old computer to the new one. I had to load the game the first time using the load option. After that, I could use the big arrow button with no problem.
If you don't see your old saves, then you may have put your saves folder in the wrong place (just guessing) and the game can't find it. So you may have to copy or move them to the right place.