Please note that I am not officially qualified to give advice on digital receiver 'faults'. You use any information provided here at your own risk. If you have any doubts, I refer you to Sky, SES-Astra, your equipment manufacturer, or your retailer as appropriate...
Assuming your sat-finder is showing a good signal, switch it to the 0dB setting and leave it in-line while you go look at your TV. If you have a signal now, then you don't have the rain margin. Switch your sat-finder back to -6dB and keep on aligning until you get it...
If you still cannot get a signal and you know something is being received, try tuning to 11.778 V 27.5 with different FEC settings. Old Astra uses 3/4 while SkyDigital uses 2/3. It may be that you're actually looking at the wrong satellite. It is very easy to do, I have managed to 'tweak' my SkyDigital alignment back to 19.2°E without realising it until I turn on and there's no EPG and CNN appears where the EPG should be!
If you still cannot get anything, take your box to a friend with SkyDigital and hook your box to their LNB. This will tell you if your box is faulty, or if it is your wiring and/or LNB.
One thing to check could be your cabling itself. In the days of analogue, some installers fitted normal television co-ax wire. This stuff will work, but only up to a point. Again, analogue works but digital will suffer. It is also more likely to work with the lower frequencies than the higher frequencies because of what it is; Sky analogue was mostly low-frequency while digital reception is more spread across the range. Is your cable the right type?
Your LNB has two "local oscillators" for the low and high band. These have to operate at a very precise frequency, however an LNB needs to be able to cope with temperatures ranging from -30°C to +70°C (if you think +70 is unlikely, imagine an LNB in the bright Tuscany sunshine, heating up with the dish acting as a reflector and no breeze to cool it down; the day may only be 35°C but roof tiles and LNBs will be considerably warmer).
Temperature has an effect on electronic devices. I had a radio that I could tune into a short wave station, and if I listened outside while gardening, it would actually change stations by itself as it warmed up. The same thing is happening to your LNB. My advice? Remove it, fit a better quality LNB!
Theoretically you could program the Digibox to the new altered frequency of the local oscillator. However if the oscillator is prone to drift, then it can drift through various frequencies and do so erratically. And, besides, unless you plan to experiment a lot, how exactly do you propose to know what the altered frequency is? Remember that a Universal LNB has two local oscillators, and there's nothing to say that both of these will change in sync. In short, either give up on watching TV for half the day, or get yourself a better LNB!
The Digibox doesn't support DiSEqC. Additionally, these devices are only useful if you are looking towards Astra (19.2°E) and Hotbird (around 13°E). If you have the prime focus at SkyDigital (28.2°E) then the secondary LNB will be pointed at a 6° offset, thus it'll be receiving... nothing.
Okay, there is no reason why you cannot fit a twin LNB and have one output go to the Digibox and the other output go to a different digital receiver that controls the dish. However the problems this could cause are many.
My advice - install a fixed dish and LNB for the Digibox, and install the rotating dish connected to its own receiver. That'll give you the best results.
For now - there's no alternative but to force a reboot. Unplug your Digibox, count to thirty, plug it back in.
This should fix all FTA channel loss until the next time it happens...
If the lost channel is a FreeView or Sky channel, some people recommend that you remove your viewing card while the box is switched off, and only reinsert it when you are asked to.
To enable or disable this, press services, 4, 0, 1, select, 4. The second option, RF Outlet Power Supply is the one you'll be wanting to alter.
Warning: I have heard that some installers will tell you that the SkyPlus is supplied on the condition that the old receiver is a trade-in. If your installer says this, read the contract very carefully. As far as I have been made aware, there is no such condition - and somebody told me that Sky are completely uninterested in the return of the Digibox, to them it is pretty much "obsolete" since the arrival of SkyPlus.
So what's the big deal? Well, you won't have a Digibox to use as backup or as a secondary receiver, and chances are that your less-than-honest installer will just flog it on eBay... money in their pocket.
If your installer walks away with your box (those who have emailed me said their installer didn't ask, just took it), demand it back and if the bloke says anything related to terms and conditions, ask him to show you this in print. Ask him to point to the contract that you have where it states the old box is to be returned (any other contract is irrelevant). If he cannot or spouts rubbish or leaves in a hurry, and won't give the box back - telephone calls are in order to both Sky and Trading Standards. It's your Digibox...
Why do you think I'm still using this old Pace 2500B instead of a version with a better tuner? On the European (ex-pat) market, a Digibox can be obtained for peanuts if you happen to be in the right place at the right time... but if not, the price is measured in hundreds.
By the way - that's not to say that all of the boxes sold overseas were 'stolen' from their owners - most of them are broken boxes that have been professionally repaired with high quality parts (which explains why the price is high) and a guarantee.
However, as in most walks of life, you do get the unscrupulous who will pass off a box they 'took' for the same sort of price. And, sadly, you get the clueless that give them their raison d'être...
By now you might be seeing the scale of the problem. This isn't a MAX232 hack by any means. I am not aware of anybody having done this, but I would imagine those that have won't be advertising it...
A further complication arises if the card for FreeView and the card for Sky are different; i.e. the Sky card has two number generator systems while the FreeView only has one.
The basic theory is the Digibox offers some sort of 'code' to the card. The card then performs a complicated mathematical calculation on this code and sends back a reply. It does not actually matter if this reply is 'right' or 'wrong'. The reply code is used for decrypting the data stream. If the reply code is correct, the data stream will decode into something understandable. If the reply code is incorrect, the data stream will remain a seemingly-random blast of noise.
This technique is often used in computer cryptography. The world at large only needs to have half of the information and - to its benefit - there is no necessity for validation of the returned codes. Simply apply the codes in the decrypt calculation, you can imply the validity based upon whether or not the decryption was successful.
I am sure you can understand that this subject is getting exponentially more complicated with every corner we go around...
...the Sky box is hackable. There is no such this as a hackproof code. But, you know, there are more NHS administrators than nurses, and there are more lawyers than bacteria...