my 53 plate vectra sri wont start?

The immobiliser system is not accepting your key and will not allow the car to start.
Either a faulty key or a faulty immobiliser.

Ocassionally the problem can be caused by a powerful radio transmitter nearby 'swamping' the signal between the key and the immo reader, if you think this may be the case try pushing the car away from the source.

Have you dropped the key or had it apart recently?
Have you tried the spare key?
If both keys fail to start it that would suggest the immobiliser system is faulty and/or needs reprogrammed.
You will need diagnostics equipment to check/rectify this.
Auto-electricians and many locksmiths will have this equipment and will come to the car, no need to pay garage/dealer prices to have the car uplifted and taken to a workshop.

HTH, good luck

fred
March 2012