Why wouldn't my Renault Laguna start?

Renault Laguna 1999 2.0 (auto) started OK, but as I started off, not all the dash lights went out, amongst which was the servo light. This has happened occasionally before on very cold mornings, so I did what I usually do, which is to stop the car, turn off the engine, and restart it, usually with the result of all warning lights going out as normal. When I tried to restart it, the engine turned over with sufficient revs, but it would not fire. About 2 or 3 hours later I returned to the car, and it started OK and has started several times since. Any clues as to what may have caused this? ECU for example? Should I be worried?