Skk q box / Toshiba smart tv keeps cutting out

[Thurcofox]

Recently brought new Toshiba smart tv(fire stick amazon),easy set up,but ongoing issue turn on tv/sky q box, everything comes on then tv screen fades to black,still have sound but no picture,so take out tv plug ,do home1080home,on sky q remote this temporarily works.Had sky engineer round yesterday replaced q box with brand new one ,same thing keeps happening ,new hdmi cable in,still scratching my head how to resolve this??.