This has happened to me mate on my vectra, sadly for me I was on the motorway when it started, didnt have a clue what was going on, managed to get it to work. A guy I know there is a mechanic, he said same as what you were told. My cam belt, fan belt and starter motor had been changed recently so the guy had the engine off then and didnt fix bolts on properly. Anyway I bought a new couple of bolts for about 3 pounds and they guy fit them on for next to nothing. scary S*** when that happens so I know how you feel mate. At least its all sorted.