Mac Mini and Samsung 4k TV via HDMI - No signal detected

Hi - I bought a new Mac mini 6 months ago and a Samsung 4k 42inch tv as a monitor. It's worked fine for a few months but now when I don't use it for more than a day, the display says no signal detected. Windows based laptop work fine with the same cable in the same TV HDMI port. I've tried using a thunderbolt to HDMI adaptor from Mac mini or Mac MacBook and still the same problem. Tried lots of reboots & sequences too. Any ideas? thanks