'The installer disc could not be found.'

Hi Loner T, one thing I hadn't done, which is the only thing I've done differently is the thing below which I've cut and pasted from Install Windows on your older Mac using Boot Camp - Apple Support I'd just followed the Boot Camp dialogue information before which doesn't mention formating the USB beforehand.

'To format an external USB drive as MS-DOS (FAT), use Disk Utility, located in /Applications/Utilities. For the scheme, choose Master Boot Record.' <= there was no option to select Master Boot Record but it worked anyway.

I've now installed windows 10 on my Mac no problem.

Thank you for the reply Loner T.

Ok, I tried both of these Alt+cmd+P+R for NVRAM & take out the power cable, wait 15 seconds, plug back in, wait 5 seconds then turn back on, for the SMC. Ran through the Boot Camp Assistant but got the same error message, I've done a screenshot for anyone not having had this error before.

Is there any anything else I could try?

Hi Loner T, here's a cut and paste from the hardware overview:-

iMac (Retina 5K, 27-inch, Mid 2015)

Model Name: iMac

Model Identifier: iMac15,1

Processor Name: Intel Core i5

Processor Speed: 3.3 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 6 MB

Memory: 24 GB

Boot ROM Version: IM151.0216.B00

SMC Version (system): 2.22f16

No it hasn’t been repaired at all. And I did buy it in an Apple store :)

The version Bootcamp Assistant I have is 6.1 according to my system report, does this help at all.