Mouse Problem / turn off in-game overlay / İ cant see invite

Yeah, you'll need the overlay on to see the invite.

While you don't say exactly what mouse issue you're having, the simplest thing to do is try a different mouse, preferably a mouse that does not allow button customization. If that mouse also has issues...

It sounds like you need to figure out what software is conflicting with in-game overlay. My suggestion would be to disable all utilities, particularly any software that controls mouse/keyboard, and then turn in-game overlay back on to see what happens. If you think you've disabled everything and still have issues, there is likely something running in the background you are not aware of - i.e. check the running services. If you don't resolve it there, you'll likely need to do a clean Windows install.