Not sure how dirty LNBs get but possibibly cleaning it might help. At one stage mine was covered in bird s@@t. When there is an accumulation of snow in your dish a pole on a broom is quite handy.
The problem I have is my Sky+HD box is so slow after a reboot. It takes at least 5 mins to get going and the green light comes on. My disc is around 50% full at the best of times. Quite often it freezes up and is useless. I'm now on the point of seeing what's available on fleebay!