Superb advice again, thanks.
Progress is being made.
Latest is I have run MEMTEST, as suggested by SD, and indeed it has found an error. Will be back out with the machine tomorrow and try to identify the memory.
I seem to remember the cost of memory is very low now? If this is the case my view would be to change all memory, does this make sense?
I don't have any spare memory, other than what is in the Inspiron 510m laptop I am currently using, presumably it will not be compatible?
BB