Alright, wits end idiot post here. Changing valve cover gaskets , I replaced fuel injectors as well as the coil packs and new plugs and wires (trying to get to the bottom of this p1074 code it kept throwing intermittently) in the process I installed the wires in the wrong firing order 7 was 1 , 6 was 4, etc. Started the car and it ran horrible so I immediately shut it off upon shutting it off I heard a loud clack not inline with a backfire just a loud click. And the car wouldn't start anymore . Since then I have corrected the firing order but upon start heard a huge grinding inline with a bad starter I assumed I damaged upon my error . So I replaced the starter . Now it cranks but won't start . I see the m and s lights flashing on dash. So I checked all the battery wiring made sure grounds looked good . It has a new yellow top optima battery not even a month old and a rebuilt alternator replaced with the battery . I have a crank position sensor I'm ready to change as well tho previous owner has said its already been changed . Really hoping if anyone has some incite of what I might check next . Xyz switch is the first symptom but given the nature of how this all came about I'm sure there is something I am missing .

Have been silently combing these forums since I purchased my D2 and all the information has been invaluable and I truly appreciate everyone involved . This is my first post ( really ashamed of the nature of it all )

 

Check the battery, it may have actually failed or not have a decent charge, unlikely as your Disco turns over.
When you turnover does the tach needle move ? If not could be the CPS.
The problem with the M&S lights is there a bunch of reasons they flash beyond battery and XYZ switch

But start simple check all your fuses and relays for damage. A loud click noise could be a relay blowing out.
Then check all your intake hoses to make sure they are secure (M&S) related
Pop the plugs and check for damage also check spark you can get an inline spark tester

 

Check your engine bay fusebox. I had a bad fuse, one of the ones with a battery symbol, and it was open, did just about the same as yours-crank, no start, M&S lights flashing, no tach movement. If you have an old school timing light you can check for spark.
Definitely charge your battery-even if it's new it can be below voltage and cause trouble.
Your engine may have kicked back and damaged the starter bendix drive, which would explain your having to replace it. You might be able to replace the bendix/solenoid and have a spare starter.

 

No experience with this problem, but maybe check (since it's turning the starter) for damage to teeth on the flexplate. Starter maybe spinning with nothing to mesh with. Or plate locked up with crankshaft locked up? Again, no personal experience with this.