Messages on Yosemite used to work fine until this morning, repeatedly asking me for my Apple ID password. Months ago I had setup 2 factor authentication for my Apple ID, but it never complained. So I set up an app specific password, Facetime took it no problem, Messages didn't and kept asking for my password. I quit, log out, restart, disable/enable from my phone, nothing works. So I disable 2FA, try again and now Messages gives me a blank window when it starts.
Is there any way I can reset it somehow ?