96 Ranger Rover 4.0 Won't restart when warm?

Hi,
I have a 1996 Range Rover 4.0 that I have had since it was new. I has 37,000 original miles and has not had the best maintenance lately. Anyhow the car startrs fine when its cold and will go anywhere once its running. However as soon as it gets warm and the car is turned off it will nat start again until it has cooled down for an hour or two, then it fine until it gets up to temp and its the same thing all over again. Has anyone got an idea as too where I should start looking in order to solve this problem?
 
Thank you

Sounds like it is time for some serious maintance. What exaqctly has been done to it, tune up wise, in the last couple of years, what octance gas are you using?
Mike

Thanks for helping!
There has been no maitenance done for years, its due for everything. As far as gas I've been using 87 oct.