immobiliser fault?

I jumped in the car as normal on 16/12/10 for my journey to work.... Would`nt start & the panel said traffic master ( sounding ) the display said immobiliser fault. Then repeatly trying for it to start no joy then left it... I then returned a couple of hours later tried again & NOW The panel indicates ( Sounding ) & display saying normal mode then auto-matic mode, but still wont start & the battery has died now, but all lights, doors & radio works still.....as my local dealer wants to clean me out money wise...HELP HELP please.....