On monday it was running great has since I bought it 3 weeks ago ,fitted a new rocker gasket on wednesday evening this morning it turned over but would not start then after a rest it started got it out of the garage turned it off shut garage door went to start car again would only turn over would not fire up, after a rest it started revervsed out of drive went down the street ,it died would not start it turned over but would not start ,as I said at the begining all I have done is renewed a rocker gasket ,any ideas please.