The PSU arrived today. I bought the Corsair CS Series Modular Corsair Gold-cert. PSU, which was slightly cheaper.
I had to take a few photos and draw a diagram of the layout inside, otherwise I would have quickly forgotten the connections! Luckily the new PSU powered up my PC and all appears to be working well. Hopefully this old computer will carry on for a bit longer until I can afford a new one.
Thank you very much for your help and advice. It saved me going to the repair shop and it was an interesting challenge getting to know more about the hardware inside my PC.