Prem El 21 will no longer open thinking I want a trial

[provlima]

I have owned Premiere Elements 21 since last September. All of a sudden I ca no longer use it because attempting to do so results in a screen appearing advising sign in required.  When I push the button another it results in another screen with two options activate this software by entering a six digit serial number  the other option button asks if i want try this software. 

It appears that the program believes I do not own the program.......How can I fix this and use the program again????????

[Peru Bob]

 activate this software by entering a six digit serial number 

By @provlima

The serial number is six groups of four numbers.

Just enter your serial number.