Help help help!

I was driving my P38 Range Rover, and it suddenly died on me, we thought that maybe it has ran out of diesel, as the petrol gauge was a bit tempramental, and didn't always give a true reading. However, we have filled it with diesel, and it still wont work. Its starts up and ticks over for about 20-30 secs and then cuts out again. We have bled the fuel lines, but still no joy.

Any advice on what this could be as its driving us mad, and we cannot afford to take it to a garage so we are trying to sort it ourselves?

Thanks

Colleen