Another car won't start thread

[FTe_XR8]

So i was pulling into my driveway last night and the car just coughed and died. I tried restarting it, it was turning over and starting but would only run for a couple of seconds and really rough like it was only firing a couple of cylinders.
I got it to start once or twice and revved it and it seemed to clear then the smartshield light would start flashing and the car would die. I decided to leave it for an hour or so then when to try it again and nothing, it wouldnt even try turn over, no "clicking" like when it has a flat battery, i could hear the relay under the dash clicking but thats it. I checked the battery and its at 12.5 volts.
I was wondering how do you know if there is a problem with the smartshield system? the light flashes like normal and when i try to start it the light goes out? Any ideas would be great as the car is stranded out the front of my house!