Q: 2008 Imac-slow

Hey rsira,

Thanks for the question. If I understand correctly, Yosemite is running slowly. I would recommend that you read these articles, they may be helpful in troubleshooting your issue.

OS X Yosemite: If your Mac runs slowly

Disk Utility to verify and try and fix any issues.

How to use Activity Monitor - Apple Support

OS X Yosemite: Reinstall OS X

Use the built-in recovery disk to reinstall OS X while keeping your files and user settings intact.

Thanks for using Apple Support Communities.

Have a good one,

Mario