Vauxhall opel omega does not start when it's cold?

I have Vauxhall opel omega 2001 4 cylinders. It starts perfectly when it's hot. If it's cold the service indicator flashes when turning on the ignition and before cranking. It cranks very well. I changed the battery ad the plugs, but the problem stills. Some told me that it may be related to Fuel pump or Crank position sensor. Others told me may be immobilizer. I tried to use a fuel system cleaner but no use. Fot the immobilizer, Ithink It's not related to weather temprature. The last things I did for the car before the problem is Changing the engine oil and the radiator is slightly leaking.|||Might be quickest and probably cheapest in the long run to take it to a Vauxhall dealer to get the codes read, the flashing indicator is telling you there's a problem.|||Your problem could be that tha automatic choke for cold start is not working. Have it checked out, its something that you need special tools to set it correctly