All my fault I'm afraid.
I had downloaded a 32bit version of Windows onto the memory stick and I think I was installing it multiple times, filling up the hard drive. I downloaded the 64bit version and it loaded perfectly.
There are a couple of outstanding issues though:
I cannot install MS Office 7 from disk. I had Office 7 on my previous version of Win10, and remember reinstalling it a couple of times but now I cannot. I input the 16-character reg code, and it is accepted, but when I press the install button nothing happens. Any ideas?
Secondly, I cannot connect my bluetooth headphones. The computer wont recognise them. They were fine with the old version.
Thanks for everyone's interest,
Chris.