What Mac do you have? Click on the Apple icon in the top left corner of your desktop and select About This Mac. Please provide the following information (you may need to click on More Info depending on what operating system you're running:
- Operating System (Version)
- Mac model
- Memory (RAM)
- Do you use CC/Mods? If so, have you tried removing them and seeing if that fixes your problem?
- What Expansion, Stuff and Game Packs do you have installed?