Discovery won't turn over!!!!

I'm at my wits end trying to find why my '97' auto discovery won't turn over!!! It was working fine, went to fill up with diesel, got back in car and hasn't started since! So, battery is fine and charged, changed starter motor (checked to make sure it was working before fitting it) and still no joy. When I put the key in the ignition and turn it, I get lights on the dash but it doesn't turn over, all I can hear is a single click from the passenger footwell every time I turn the key. I read on some thread that many other people had this same problem and that taking out the spider unit behind the central dash does the trick! That's all fine and dandy, but on taking out the dash, I found that I don't have a spider unit just under the radio housing. So, what now? Any suggestions would be very welcome. Oh, I've also checked the earths.

you could turn it over with a forklift

Thanks, I will try that if I don't get any other suggestions

Immobiliser
Starter inhibit switch
Starter Motor Relay

Starter motor is fine as I replaced the old one which on testing, was working fine

does it think its anything other than park on the auto box? they wont start in gear i think.

I've just had the same problem. Check to make sure your alternator hasn't seized sounds daft but it puts resistance on the belt and more strain on the starter motor causing it not to turn over. ive just fixed mine today after 6 hours of head scratching! Or simply slip the aux belt off (dont leave it running because the aux belt also runs the water pump

If that doesn't work put your transfer box in n and gearbox in n too just in case it is sticking in gear

I had exactly the same thing on my auto 300 ,lights on dash but just a click when turning key.Tried everything for days until I cured it. On the starter motor there is a wire with a spade type connector on the end ,I gave it a bit of a wriggle and she started up! since then its done it a few times so I just pop the bonnet and give it a wriggle and were of again.

as post 4 . plus you could use jump lead direct to starter motor just to prove its working (bypasses all inhibitors that way so don't be in front in case gear stuck!!)

Any updates teamholden?