Q: How do I login to my iMac when it rejects the same password always used?

I use the same login password for my iMac and Macbook Pro however, the login password no longer works for my iMac. It still works for my Macbook Pro... I checked all the silly things such as caps lock etc. to no avail. Does anyone know how I can access my iMac? It says I can use my Apple ID if I forgot my password (which I didn't) and I tried using both my Apple ID and password and that didn't work as well...

Any help would be greatly appreciated.

Thank you so very much!