Hi Carolyn,
Is there a particular error message that you get? Have you been able to install on another machine?
You might like to look at the following document https://helpx.adobe.com/creative-suite/kb/unable-validate-serial-number-ccm.html
This gives general advice regarding serial numbers.
If the problem persists I would reach out to our support chat who can check the s/n for you (best not to do this on a public forum).