After only 90 days of Directvstreaming, TV Screens Going Black

After 90 days of trouble free service, just began having to unplug receiver boxes to reset 2 TV screens to regain picture. Beyond annoying and may force us to return to cable tv.  Gateway modem is only about 20 feet away from each tv - which are in separate rooms. One wallboard wall between one tv and modem. Two walls between modem and other tv. No problems for first 3 months after installation. Gateway modem is positioned between my desktop mainframe and monitor and small speakers. No problems with computer because desktop and monitor are connected to mainframe by ethernet cable. Not easy to relocate Gateway modem. I am  challenged technically. Is there a very easy to install wi fi booster device that is relatively stable? Good brand? How do I hook it up and where do I hook it up? Thank you.