VW Beetle will not stay running

[02beetlebug]

2002 Beetle 1.8t will start, but then dies. I have been having issues with the car not starting or starting then not staying running for awhile. The car has also within the last couple of years on occassion ran rough after starting and will serge so to speak. Today my car ran great and then I went to start it and the car would start and then die. I noticed that the immobilizer light and now it flashes when the key is in the ignition. I have been using the same key for the 8 years that I have had the car.