Hi adw1960,
I have exactly the same problem with my D series - FH2 model. After spending quite a bit of money calling the siemans "tech support" to find out how to remove the case....i gave up. Not least because they said (repeatedly) that they would call back.
I think your right about it being a heat problem, and these models seem to be well known for having loud fans - so cleaning won't neccesarily make it much quieter but will stop it turning off!!
If you find (or have found) the "trick" to removing the case - please post back here - and i shall do the same..
-----------------------------------------------------
As a side note, i have to say that after paying £1300 for my laptop, to have it rendered as good as useless - for the sake of a good clean is pretty sickening.
Whilst i love the computer - i cannot say the same for the customer support, for a multinational co. such as F/S, not to be able to put me in touch with someone who can remove the back of a laptop THEY make is frankly disgraceful.
------------------------------------------------------
Sorry,
rant over ---- any help (@ all) gratefully accepted