RegCleanup

Hey everyone! So I've recently been having problems with my Windows computer (dell g7 laptop) and I remembered that I had changed some reg stuff. I was looking for a way to revert the changes or fix it. CCleaner looked like a solution. So, I downloaded the program and did the Reg cleanup thingy. Unfortunately, after doing so, my computer started crashing a lot and programs wouldn't open. Even task manager wouldn't work. How can I revert the changes? I made a backup reg file but when I tried to import it with reg edit it said that it was incomplete/didn't have enough permissions. What should I do?

Thanks!