MGF immobilser wont disable

I have a 98 MGF VVC with Mems2J / 5AS. It has been working fine but currently is refusing to start - or even crank.

The Key fobs door locking / indicators etc all appear to be working normally. Battery health all feels good ( I have charged to be sure and tried with a jump pack connected with no difference)

pscan can talk to the 5AS ok - all seems normal as far as I can tell. It can talk to the Mems OK. The "Security input" is oscillating low/high and in the extra features it reports correct EMS is being received but immobiliser must be disarmed to read status.

Any suggestions ?

If it's not even cranking then I would be having a look at the starter motor, starting with checking the connections. 

‘40 is going along the same track as I would. The solenoid connectors are suspect & certainly on a car of your vintage; my car is the same in all aspects. I have changed these for better crimps, having experienced exactly the same problem & from a dunce to a dazzling in ten minutes.
I am fortunate in having a pit & so my ten minutes might not be applicable to you, if you are not so endowed.
M

If you do not have red LED blinking on the dash while you are trying to start the car, then it is not immobiliser in question, but something else. Starter, as said, would also be my first port of call.