Will cs5 work on Mac Yosemite?
Upgrading Yosemite breaks the CS5 install, so you need to uninstall/reinstall CS5 to fix it.
Update Yosemite to 10.10.1 Then reinstall.
The install sets CS5 back to 12.0.0, so don't forget to run updates.
It should work after that.
Gene
(If my answer worked, mark it as correct.)