My S reg Vectra 2Ltr DI Diesel turbo Won't start?

My preheat light doesn't come on when I switch on the ignition but all the other lights come on and go out as they should. The engine will turn over but won't start. The engine warning light doesn't stay on so I don't think that the problem is electrical (What do I know?) The glow plugs don't work but when I took each one out and tested them they were ok, I took one of the injector pipes off and there was fuel coming out but it didn't seem to have much pressure. Thank you in advance.