iMac (27-inch, Late 2013) I bought this recently. It's mouse does not work as it used to, e.g. I can't toggle up and down

Hi kkfromowingsmills,

Thank you for contributing to the Apple Support Communities.

If you're not able to scroll up and down using the Apple Mouse that came with your iMac, try these tips first:

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.

From:

Troubleshooting wireless mouse and keyboard issues - Apple Support

Best Regards,

Jeremy