Can't login to iTunes. Keep getting an error. "There was a temporary problem completing your request. An unknown error occurred (5002)."

Greetings, Jayhawk116.
Thanks for joining Apple Support Communities! From your post, you're having problems logging into iTunes on your iMac. I'll be more than glad to help you with this.
If you can’t connect to the iTunes Store

On your Mac

1. Make sure that you can access the Internet on your computer.
2. See if your computer meets the iTunes minimum system requirements.
3. Check that your operating system is up to date.
4. From the menu bar at the top of your screen, choose Apple () > Software Update. If you don't see Software Update, choose Apple > App Store and click the Updates tab in the App Store window.
5. Make sure that you have the latest versions of iTunes and Safari.
6. If you have a firewall, your settings might not let you connect to the iTunes Store. Learn how to set up your firewall.
7. Connection issues are sometimes caused by keychain issues. To reset your keychain, use Keychain First Aid.
8. Contact your Internet service provider, and make sure that these ports and servers are turned on for your network.

If there's still an issue, get more help.

Have a great weekend!