Thought I'd have one last go at it before calling it a night and yep you guessed it...
IT LIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIVES!!!! Wooooooo.
With a little help from my son Alex and my supportive wife Kath who stopped me going insane I finally managed to get her up and running. My guess is something was loose somewhere and was just causing the machine to have a bit of a strop. I can't believe how silent it is now compared to what it was before either, even at boot which used to be ludicrously noisy.
Just about to install my first set of Geforce drivers so will report back on how it does with games when I can.
IT'S ALIVE, IT'S ALIIIIIIVE mwhahahahahaha!
Her face is tired. Leave her be ffs.