Thanks for weighing in with this topic. After watching temperature fugures closely during the last incident I now know almost exactly what is going on.
The fan only responds to the CPU diode temperature. When this hits 80 the fan will kick in, it will cut out when it dips below 70.
The lowest temp I've seen standby cut in on is 85, If I contimue to try and watch the film the GPU has gone as high as 90 with the fan still not kicking in. I decided not to stress things furthur.
I am using the laptop to watch SD movies mainly but I watch 720p stuff through the HDMI and occasionally 1080p so it's an issue.
I think I'm a victim of making my laptop efficient enough not to stress an atom CPU when watching 720p, in a way I'm slightly proud of myself. :-D
It's been suggested that I send it back into warrenty and I'm wondering what temps your GPUs run at, if 85 is in range for GPU then it is something wrong with the mainboard and I'll send it back in safe in the knowledge that there is a real problem.
I'm also wondering if different graphics drivers may help if you're using XP what version are you using