Hi guys....need your help please!!!

Drove my car home last night about 20 miles no probs - came to my car this morning.....it would turn over quite happily - just not start. Not even a chug. Odd I thought! Then just before the battery died after a while of trying - it suddenly started out of the blue.

So I went to the corner shop - left it running outside - drove home - parked up - turned it off - immediately started it again - fine no probs.

Then I loaded my car up with a few bits & pieces for an engine change on a mates car....came to start it...nothing...zilch...narda!!!! (

Been trying on and off all day inbetween engine changing - deduced that fuel is not coming out of the pump.

So am I right in thinking that this is one of 4things.....

1.) Knackered diesel pump - rare for them to go but possible,
2.) Pump is drawing air rather than diesel - possibly can be tested by feeding the pump with fuel from a bottle of diesel rather than the tank
3.) Fuel Solenoid stuck - not entirely sure its this as you can hear it click when you switch the ignition on
4.) Possible immobiliser problem related to the pump in some way??

What do you guys reckon in your experience...anything else it could be??? :'( :'( :'(

This car has never let me down up until now!!!