I was able to use Photoshop CS6 beta on the same machine as Photoshop CS2 without any problems. I uninstalled the beta and installed the release version of Photoshop CS6. When I ran Photoshop CS2, it "hung." The small initial popup that is supposed to show the names of the development team and the start-up status messages shows up -- but only as a white rectangle.
I rebooted the computer and tried again with nothing else running -- and got the same result.
Thinking the installation program might have a Repair option, I launched Control Panel and selected Add/Remove Programs. Photoshop CS2 does not appear in the list of installed applications.
How can I fix Photoshop CS2?
You will want to reinstall Photoshop CS2 from your installation media.
As for why it is no longer listed under Add/Remove Programs. Do you regularly use some type of registry cleaner/system optimization program?
I tried a program called "Speedy PC" from Pareto; it could be the culprit. (I had not tried to run PS CS2 after installing the release version of PS CS6, so I don't know if it stopped working as part of the CS6 installation -- or because something the Pareto software did.)
Installation disks, installation disks -- I know I had them when I installed the software six years ago......