@f1ee7a25 Okay, so it’s in the setup stage, hasn’t properly started replacing files yet, and it isn’t throwing an error code. Tell you what, boot recovery mode and rePARTITION and reformat the drive, then try an install again. I feel like there’s something locked or corrupted or something that’s making the installer fail when it begins trying to manipulate files on the drive. 

 @531f5a72 I'm trying re-setting the parameter RAM next, then will look at partitioning. (My attempts to make a bootable Sierra install USB pen drive have failed also.) 

 @f1ee7a25 Yeah, with the later versions of macOS, you need to install a full environment to an external hard drive and then boot the target machine from that, then install to the internal drive from an downloaded installer on the external. Lots of problems trying to just do it from a pen drive. 

 @531f5a72 Ah that's interesting - bit of pain but I might give that a go. Partitioning in half didn't work - one half gave same errors as before, other half gives odd App Store type download failure errors. I wonder if there are TWO issues going on here, faulty drive AND something with certificates. 

 @f1ee7a25 I'm wondering whether it might be bad piece of RAM, or possibly a mainboard issue.You could try installing Ubuntu on it, see whether their hardware diags report anything. Linux tends to be more transparent than macOS about what state the hardware is in. 

 @531f5a72 Oh that's a thought! Thank you, I'll have one more crack at installing MacOS from an external drive then look at that. 

 @f1ee7a25  Don't forget, be booted from the external to install. 

 @531f5a72 Roger!