Well got some new info.
The present motherboard is a replacement, this problem has poped up before and the laptop was taken to a 'professional' who replaced the motherboard.
This solved the problem for a period (not sure how long) but obviously not permanently.
So I'm still down to trial and error, I can't see any apparent damage on the motherboard.
The heatsink moving causing the processor to over heat is possible and I shall look into it but I wouldn't expect it to happen instantly and would expect some kind of warning.
In anycase I won't let this laptop beat me