Icloud sign pops up with my old charter email (grayed out/can'd click on it).

I had a charter email account. I am in process of leaving charter. I set up my iCloud email account & it works with my password on my iPhone.

I thought I had correctly set up iCloud email on my Dell desktop. However, when I open my Dell the opening screen comes up as usual but then the "Continue to Sign in to iCloud" pops up. Above the password sign, in grey, not clickable, it says "Enter the password for on....sam@charter.net. I type in my apple password and get message invalid Password. What do I do?