Sadly, there's not much you can do internally in this case. Its' time for a new unit.
As for preventing it the next time:
Speak with your cable provider and see what they say first.
If they push back onto you, go to a good electrical supply house pickup a copper grounding rod and the needed clip and wire. Hammer the rod into the earth near the entry point of the cable into your house. Make sure you know whats in the ground where you are planing to hammer the rod into i.e. [http://www.digsafe.com|DigSafe]. You will need to ask the cable operator to come in to cut and splice the cable for the grounding connection and attach the heavy gage (#8 or #10) copper wire to your rod.
This should prevent the charge from entering via the cables connection. You may also want to speak to an electrician on checking your buildings electrical services ground. Even still this will only stop entry it won't stop a direct hit.