Can't enter wifi password

[Dlass]

I'm getting rid of a MacMini late 2009. Used Recovery and Disk Utility to erase the hard drive, and now I want to use Recovery to reinstall El Capitan. I choose to do that, and it complains that the internet isn't connected. No prob. I select my wifi router, and it asks for a password. But I try to type in a password and no text appears in the password block. I can't type in my wifi password! This is nuts. How do I link to my wifi router after a disk erase?