No sound, and picture appearing briefly every few seconds (HDMI)

I'm getting no sound via HDMI on my HDR-Fox T2, and the screen is also blank apart from brief periods of a few seconds when the picture appears before disappearing again. I've tried power cycling, and also pressing the V-Format button multiple times, but neither has helped.
Any ideas?

Ian Manning

Thanks for that. I currently have the HDMI going through a splitter (to resolve some other problem which I can't recall!), and after disconnecting and reconnecting the splitter I got sound and picture back.