I have run some tests, first thing was to unplug the ethernet, this seems to have worked, hasn't crashed again tonight, when I tried to plug it back in, it crashed my router! So I have swapped ethernet cables with a better one. This seems to run fine.
I played GTA for an hour, no crashes. So its nice and hot, and now I have it folding@home, as more of a heat test. And its holding up fine...
I also turned it off, vacuumed the death out of it, and re-seated the HDD.
And personally I am one of these people that would rather a new one, over a expensive replacement or repair. Same thing happened to my dad with his watch today, was told it would cost him $369 to fix (by Citizen), he only paid $500 for it!
But anyway, I have many theories, I am just narrowing them down as I go. It could be a bit like a 'cold start' thing, its been abnormally cold recently, and starting it up from cold might stress it. Cause its been fine all night now. Folding away like a dream, GTA ran fine too.