I imagine there are many instances of the correct answer to my question here, but I have little for diagnosis besides the engine sound.
I have a 1.4l petrol Toyota Corolla 2001 model. The car was serviced two or three months ago and it was mentioned to me that I should have the spark plugs changed (perhaps they were trying to squeeze me, but they might have been right). I haven't changed them yet though.
I hadn't used my car in about a week and now the temperature is low (just above freezing). The engine will turn and I hear some gentle "popping". I assume some cylinder ignitions are taking place. The sound is irregular though and it doesn't seem to quite be able to start.
The oil is low, but within the limits (it is possible the service centre didn't put the recommended oil in). I have half a tank of petrol.
One more thing, in case it may matter. I recently replaced the lower radiator hose, which involved draining and replacing the engine coolant. The reported engine temperature was fine afterwards.
Here are a couple of links to engine starting sounds. I'm guessing that a seasoned ear can diagnose the fault from this (fingers crossed)
Thanks very much for any help people can offer!