starter motor problems

hi guys
ive got a m plate v8 disco and for some time i have had an intermittent problem with my starter(or atleast i think its my starter).
i put the key in turn the ignition,all lights come on and turn it to crank but nothing happens..if i leave it held in the crank position for anything up to 3 mins it sometimes turns over.sometimes i get in it and it starts straight away.i have checked all connections on starter and they seem ok.the live battery feed has the nuts up tight but the stud moves slightly im not sure if this is meant to do this.the battery is good.
could it be a problem with a possible immobiliser?? i have no aftermarket one fitted but did the discos have them at that age?
i hope someone can shed some light as the next thing outta the toolbox is a hammer.. cheers lads

Use a mutimeter, powerprobe test lamp etc to check that when the key is turned to the 'crank' position the starter solenoid feed is turning live. If it is then you are looking at a starter problem. If it isn't you are looking at an immobiliser, ignition switch or wiring problem.

Judging by the fact that the stud has movement in it I would say it's the starter thats at fault. A good auto electrician should be able to sort you out with the bits you need to repair it or repair it for you.