Hyundai Matrix car won't start

The problem has been going on for a month. It has trouble starting, I know it's not the glow plugs as it has more problems when hot than cold, and the plugs were changed about 10 months ago. Once the engine has started, there is no indication off bad performance, it is only the starting of the engine. It sounds like there is no fuel getting to the engine, but when it does start, it is perfectly fine. It now has given up altogether. The battery is good, the fuel filter is good.
I have been told it might be the injectors, but if it was these, would it not give me bad performance when running ?? And all three would have gone at the same time. Unlikly.

Any ideas???