Photoshop Elements serial no longer accepted?

I am trying to use an installed from disc copy of Photoshop Elements 15 I bought new with my Mac about 5 years ago. I have installed it on pc laptops before, but it is no longer accepting the purchased copy serial giving it a red x when I try and enter it. If adobe thinks that after 30 years of being an adoring customer since the put in LAYERS back in PS 8 I am going to start paying MONTHLY for the privaledge of using their software they are SORELY MISTAKEN. The fun I having making hilarious anti trump memes is just not worth it to me. Why exactly isnt just buying their precious software good enough anymore? I hope someone can help me with this.