Damn it

My VL got broken into and attempted hotwire, i started it after this happened but only once. I havent started it for about for about 3 weeks now, the cars turning over but is not firing up anymore. My ex-mechanic friend had a look at it and we cant identify the problem. If anyone has any idea what could be the problem please feel free to leave opinions and advise, it would be greatly appreciated.
Many thanks