I had that happen to a Vauxhall once after the battery went flat so if the original garage disconnected the battery they could have caused it. However there should be a procedure n your handbook to restore things to the way they were.
Alternatively, get an independent report on what caused the problem from an auto electrician. If it was caused by the original garage tell them to fix it. If they can't/won't have the Vauxhall dealer fix it and then take the original one to the Small Claims court. As a courtesy I'd let them know that you were going to do this. However the net of it is before they had the car it worked and now is doesn't - so they should fix it regardless because it happened while in their charge.
t
May 2007