accountsd / com.apple.icloudhelper.xpc wants to use icloud

Messages keep coming up and the password for my icloud account will not work. I don't know what other password it could be as I've never set anything else up that I remember. Many mac functions aren't working - Safari freezes, mail can't connect, system preferences freezes sometimes and have to force quit. Could it be my upgrade to El Capitan recently?

Mac is an air, 2015