What operating system?
Have you used that serial number previously?
Creative Cloud or standalone?
How many characters in the serial number? DON'T post the serial number.
Is it a Lightroom 5 serial number?
It is a LR% serial number from a purchase in Dec 2013. I just got a new laptop and want to use it for editing. I logged in to adobe and found my serial number, however entering it comes back that it is invalid. I double checked so I am sure the numbers are correct. Do I maybe have to uninstall my LR5 that is on my other laptop?
I’d leave LR on that first laptop otherwise you might never get LR working on any of your computers.
You can install LR on up to two computers and the invalid check wouldn’t be instantaneous even if you were trying to install it on a third, so if it is coming back invalid immediately then there’s something about the serial number digits you’ve just entered that it doesn’t like without even going to the Adobe servers to look up anything which it may never do, anyway. There should be 24 digits beginning with 1160.
Is your serial number for the same type of LR that you’re installing? By that I mean is it educational/student/teacher, cloud, team, enterprise, or the normal individual for $120-ish?
Did you purchase LR from Adobe or from somewhere else and just registered it with Adobe?
If you can’t figure it out, maybe start at chat session with Adobe support on Monday and see if they can figure out why the serial number isn’t working.