+1 with what Ian says.

Occasionally I have a similar problem where I get nothing whatsoever from my projector through my Oppo / HD621. More often than not there's been a problem / power interruption / update etc with my SKY box - which then upsets everything else in the chain.
The only way to fix this, much to my annoyance, is to physically disconnect every piece of equipment (so that they're all, in effect, isolated) and remove the power from each link in the chain as well. I mean - switch off & remove the power cable so there's no chance anything's on standby. This then removes the possibility that anything's "hot-plug" connected, or there's anything dodgy in some memory chip somewhere. Then reconnect, slowly, one by one and it should all be ok.
It's a total pain in the *ss and happens (for me) once a month or so, but....

The other thing to do is also - as we've all mentioned (and experienced) - try to keep the firmware up-to-date. Although, having said that, and slightly O/T, most of us who've just migrated to the latest SqueezeServer 7.6.0 software are regretting it ! ;-)

Good luck !

Trinnov Altitude CI-12; Meridian 861v8 + ID41 + UHD722v2 + 271, 2*SE-update DSP8.2Ks, SE-update DSP7200HC, 4*DSP3200, 4*DSP33, 218, 251
JVC DLA-NZ8; Panasonic TX-P60ZT60E; Lumagen Radiance Pro 5348
Roon [13i7 Win.11 NUC]; SKY Q; Oppo UDP-203EU; AppleTV / Fire Cube / Roku / NVidia