Thanks for your reply.
That's a very strange resolution, but I trust it worked and in some ways it makes sense.
I'll try and sort some more cooling out in my case, and considering I have 8GB RAM in 4 separate sticks, that may be the cause of the problem. The RAM does have heat spreaders on each stick (Kingston HyperX), so maybe the heat just needs blowing away!
I'll update once I have the problem sorted, so to benefit other people.