2 computers using photoshop

I own a valid photoshop cs5.1 version. In the pass I had it installed on two other machines with different email accounts. those machines became obsolete ,trashed. And the email accounts are gone as well.

Upon attempting to log into photoshop now it brings only a pop box where some of the information says that my serial number is already activated on two other computers. 

I need a solution to be able to use my product again.

Please advise thank you.