You have proved box works ok elsewhere.
I would not expect 20 yr cable and lnb to last that long without issues.
Here is an old thread elsewhere.
"
Just before Christmas we had a few big storms with lots of rain and high winds.
During the storms I was not surprised to see Sky breaking up, however after the storms had finished and the skies were clear, I still had no signal from either of the two channels. Previously I was used to signal strength of approx. 90% with signal quality of 100% on both channels.
Following a number of reboots (including disconnecting the LNB cables from the back of this sky dish). There was still no signal and neither of the channels were locked.
Given it was almost Christmas and I would not get any repairs for a week of or out of desperation I prodded the dish with a long stick, apart water falling from the sky dish, in particular a large drop from the LNB, the signal returned to normal immediately. I did not prod the dish hard enough to move the dish.
Now ever time it rains I lose both channels? Are there any known faults with water getting into the LNBs? "
And you wonder why cable and lnb give issues ????