Last night I stopped outside a shop returned to my car 5 minutes later and it would not start, all electrics came on but the starter motor wouldn't turn and there were no noises coming from under the bonnet at all, I checked a few fuses etc but everythign seemed ok so I left the car and got a taxi home, I returned to the car this morning and it started 1st time, I've been driving about in the car for about 3 hours and eventually got home, a few minutes ago I jumped back into it to go to the shops and once again absolutely nothing is happening when I try to turn the engine over -all electrics are working, battery power is fine, it's as though something is stopping the ignition signal getting through to the starter motor, I tried my spare key and that gicves the same results so I suppose the keys are fine, could the ECU be knackered?
TIA.