Hi naiyrou,
If you are having scrolling issues with your Apple mouse on your iMac, you may find the following article helpful, in particular this portion:
Mouse doesn't scroll up or down or side to side
- For mice that have a scroll ball, refer to How to clean your Mighty Mouse.
- Check the Scrolling speed slide-control at the top, and make sure the “Scroll” checkbox is checked.
- For scrolling side-to-side, make sure the application you’re using supports side-to-side scrolling.
- Remember, scrolling is done with one finger, and navigating is done by swiping side-to-side with two fingers.
- Navigating moves from page to page in a document or internet browser unlike scrolling.
Apple Support: Troubleshooting wireless mouse and keyboard issues
http://support.apple.com/kb/ts3048
Regards,
- Brenden