When the progress bar gets about half way along, the screen just goes blank white and nothing further happens. I cannot log in.
I have tried resetting the PRAM (or NVRAM) and the SMC and reinstalling the OS (I think it is High Sierra).
I appreciate this is an old machine, but was hoping to retain it as a “back-up” as the old accounting software I used is not compatible with Catalina and there are no plans to upgrade the software. I still need access, however, for at least a year or two.
So any thoughts about what is wrong and whether it is fixable would be much appreciated?
Definitely a GPU failure. There are instructions for disabling the discrete GPU and just running off the integrated GPU. If you’re handy with hardware realmacmods.com has instructions. When you disable the GPU you won’t be able to use an external monitor.