Electrical Fault?

Hi Guys
Newbie here...so be gentle. After some years of faithful service my 90 has developed a worrying habit...upon switching on (both cold and after running) the temp guage flys over to red and the engine turns over but doesn't start. My local engineer, a reliable and trustworthy chap, consulted a man at the local 'Local Land Rover Dealer' to be told 'Oh, it's common for 'that' to happen...they're very susceptible to 'that''...without explaining what 'that' was other than to point my guy in the direction of the underseat electrics, which were, apparently, a bit mucky. After cleaning the problem did go away...for a while. Now it's back. Trusting my 'Local Land Rover Dealer' as far as I can throw him (and I'm a big lad) I thought I'd ask you bunch of fine gents if you had a clue as to what 'that' might be...and how to get it fixed. Any thoughts for the technical amateur I am?
Appreciation, in advance, for any help.
Cheers
Brian

Looking at the 2 issues as seperate problems, it could be a fuel line system, if the engine turns over but won't start is it getting fuel? Does it start eventully? If so, after what and how? What engine do you have? Does your engine have one of these computer things on it?

Is there any reason to tie the temp guage and non start together? I think the temp guage is "that", I know land rovers tend to have guages that don't actully work so well, so the LLRD may have been reffering to the guage and not the other fault.

Thanks for the advice Discomania...ace nomenclature by the way!...The two problems always occur together and whenthe temp guage is not in the red it will turn over and start OK. I've been advised it may be oil in the wiring harness under the drivers seat which is indeed oily to buggery...apparently a design fault acknowledged by Land Rover.

Cheers

Brian