1999 Fiat Panda car won't start

The car was running ok. The next day I tried to start it, the engine turned over a few times then stopped. I checked battery, it was ok at 13.5 volts. I checked gear change and could hear it change in all settings. tried again. When I switched on there was a short buzzing noise coming from somewhere, but it was difficult to locate due to the short duration. I tried again and it only turned over one or two revs, then there was a slight thump, as though a bolt had been shot. I walked away and tried next day and had the same response. Put a OBD fault tester on it but this did not show anything helpful.
I wanted to move vehicle out of the way, but it seems stuck somehow, and will not roll. When I first switched on prior to cranking the engine, all dash lights come on and go through the check sequence ok with no warnings, but the service finish advise shows, and has done for a while, because it was not reset after the last service. Battery is re charged back up to 13v all other electrics work OK. Any ideas.