P Reg '96 Citroen Berlingo Van - Immobiliser Locked?

Left the van standing for about 4 months and when I went to start it the red and green light on the immobiliser are permanently on. Charged the battery. Entered the code and turned the ignition. Diesel is getting to the pump but not from the pump to the injectors.
It does turn over but wont start up and both lights on the immobiliser are still on. So frustrating and need the van back on the road urgently. Help please!!!