You just need it re-aligning. If Minidish, critical positioning.
If you want to cure completely, 80cm dish and lowest dB spec you can find (like 0.2 or less)
Unplug it leave it for a few secs then plug back in. I regularly lose one of the signals.
IMHO the box is very quality and goes wrong on a weekly basis. I never bother ringing SKY to get someone out to fix it as I have more chance of guessing one of the celebs on thru the keyhole! They are on some sort of commission for not arranging call-outs I reckon.
I keep meaning to ring them to cancel as SKY have had enough of my money over the years.