Thanks Jamie, i will re-seat the ram and see if that has any effect, other than that maybe it needs a replacement HD and no mate, it is never running whilst in tow.
The strange thing is that after about 15 minutes it seems to be working quite well.
Leon
Just to add to this, I have a lot of photos on my machine as that is what I do, usually they, the photos load instantly for viewing but now notice that they pixelate for a few seconds, then come clear, Ram could well be the issue as you have suggested