Can no longer connect to Remote Computer

TeamViewer had been working great until today.  Last time I used it was about a week ago.  I use it to help my dad with his Tech issues.  Today it will not connect.  I tried shutting down and restarting each computer. I tried closing all running TeamViewer processes and re-installing on both computers.  THey are both PCs and he is running Windows 10 and I am running Windows 7.  I am not super tech savy myself, but can anyone help me?