I had Lightroom on our previous desktop and on my daughter's laptop.. My daughter uninstalled hers from her laptop. So it was only being used on my desktop. We just got a new desktop about a month ago. When we got the new computer, I downloaded the latest version of LR from Adobe, and used my serial number. (It kept making me add the serial number every time I used it, which I thought was weird.) Now it won't let me develop any photos and says I need to get a license or something. I don't know what to do now... I guess it needs to be deactivated from the other computers and activated on this new one?
Which version of Lightroom does this involve (the version your daughter had)? It sounds like you might not have a license for the latest version and it was just running in trial mode for awhile until the trial ended... making you think you needed to activate it every time.
If your license is for an older version then you need to acquire that older version and install that. Serial numbers are only valid for the version for which they were purchased.