Cut out and now won't start.

I have just fitted a new fuel tank. I had the vehicle running and ticking over afterwards. Then it just cut out. Now it won't start. It has got a new fuel pump relay and fuel in. It a golf cabriolet gti 84. After a little investigation I have noticed the fuel return pipe has been blocked ! This doesn't seem right to me. I am thinking a fuel issue or air lock?  The pump runs for a few seconds after ignition is turned on as it should. Has anyone else had something similar happen?

If it is a K-jet which I assume if she's a GTi, then you need the fuel return line otherwise your system pressure will be far too high and there will be possibly be reduced flow to the injectors.  Its a continuous injection system so fuel is constantly flowing through the supply and return lines.

How the hell has it been running ? It hasn't been driven on the road but it has been ticking over and revving ok. I think the in tank pump has failed causing the cut out and not starting so I will try that. 

It might not be the full cause of your problem, but certainly you need to get the return flow to the tank or your system pressure will be high.  Once you've got that sorted, see what happens and then fault find further.

You may have worn out the pump by effectively dead-heading it with a high pressure/low flow condition for a long time.

Ok thanks for the input. I will post again once I have the car up and running. The car has been of road since around 2008. Also been messed around with by others since then. I am in the process of putting it back to standard and getting it on the road.