The service light has probably appeared because the airbag light is on, to indicate you need to visit a dealer.
The car needs to be put on a diagnostic machine to find out the cause of the airbag light.
As cheeky has said you have a fault in the airbag system and the service light is telling you to fix it, the most likely fault is the electrical connections under the seat, for more information join this forum, other people have easily fixed this problem.......