Hi, welcome to the forum!
First things first, does theengine turn over? How fast? The 2.5Di requires quite a fast turn over to start. Is there any fuel in it? (I have to ask

)
The most likely cause is the fuel stop valve on the back of the injection pump is not opening, hence no fuel to the pump. This could be for several reasons, it's just failed, a fuse has blown, the wire has fallen off/broken.
Alternatively, if you have one, the fuel lift pump could have failed. Its at the back of the engine, low down on the passenger side.
Are you still getting all the ignition lights on the dash when you turn the key?
Steve