@ElsieSimming
So all of that happens even before you try to load a saved game? In that case, it can't be a problem with the save so we have to look at the game itself or the way the game interacts with your updated system.
First let's see if you can use the game disc at all. Insert the disc, don't start the game but open the disc itself in the Finder. Now you should be able to see the content of the disc. If so, the disc at least is not the problem.
Secondly: MacOS works with users; even if you're the only one using the machine, you're still just one user. It may be that during the update you somehow created another user (with probably the same name, otherwise you might have noticed it right away). The game is licensed to one user only (the one you 'were' when you entered the serial key during installation). If the a new, 'other', user tries to start the program the Sims will refuse you access — even if the name of that 'other' user is the same as the original one. I understand you already took out all your EP's so maybe trying a full re-install (were you have to enter the key again) will solve the problem. Try to do that the proper way by first un-installing the current version, then restarting your machine and finally installing the game anew.
Btw: if a program/game hangs like you described you should be able to close the offender by pressing Cmd-Alt-Esc simultaneously (Command-Option-Escape). You get a list of all running programs; select the non-responding one and click 'Force Quit' to kill it. This works almost always, even in the worst of instances!