Hi... I'm new to this. My hard drive failed and I had to have it replaced. Because of that, I have to reinstall all my software, inclusing Photoshop. The version I had is CS5. I found my serial number, but I am getting a message that I cannot because I don't have a version on my computer. I don't have it because this is a new hard drive. I'm not sure what to do.
It sounds like your version of CS5 is an upgrade, meaning you purchased it as an upgrade to a previous version. The message you are seeing is likely telling you it cannot find the older version on the machine In this case it will provide a list of earlier versions for you to select from and some input fields for entering the serial number of that older ("qualifying") version so that you can prove you qualify to use the upgrade version.
If this doesn't seem to relate to your situation then you will need to provide more details regarding the messages you get when you try to install the CS5 software.