Page 1 of Sky HD Issue

Ok i have Sky HD about 5months now and since i`ve had it i`ve had internitting problems with certain channels (Sky One, Sky Two, Sky Three, Q, Kiss) to name a few. What happens is they sometimes dont come on, all i get is the No Sat Sig Message but i have full good signal on both inputs, I`ve made sure dish is alligned, also got lnb changed by friend who is an installer but i still get this prob. He hasn`t got a clue and we even changed the HD box but with same results. My cable runs are a little above average but not extreme. Has anyone ever had this or simular and could help me? Any help will be much appreciated.
Cheers

i also have had this problem, had box changed twice to be told they are reconditioned boxes once your first one has a problem, after paying £200 and a huge fortune a month to sky and having failed recordings and messages on screen have binned sky as it is a waste of money.