I have an old Photoshop CS3 that was installed on a desktop that crashed and is not even bootable. I now have a new desktop with windows 10 and I installed it and it is working. The activate is dimmed, but I am unable to register it. It says there is

Please read https://forums.adobe.com/thread/1499014

-try some steps such as changing browsers and turning off your firewall

-also flush your browser cache so you are starting with a fresh browser

-check hosts file for blocked entries https://forums.adobe.com/thread/1912777

An idea that MAY work to install and/or run old programs in Windows 10... works for some, not for others

-http://www.tenforums.com/tutorials/15523-compatibility-mode-settings-apps-change-windows-10-a.html

-or Run as Administrator http://forums.adobe.com/thread/969395 to assign FULL permissions may help... says Encore, but sometimes required for ALL Adobe programs (this is NOT the same as using an Administrator account)