jephree
many thanks for your reply.
I'm pretty sure you're right about a hardware problem but I can't work out what it is.
Everest suggests normal temps.
I have replaced my power supply and cpu cooler.
Memtest 68 suggests the memory is OK. The cpu is not overclocked.
Not all errors seem to be 1003 although I'm not sure what the other values mean. I will post other error readings if they would be of use to you.
Could it be the motherboard??

Thanks again

Simon F