Thanks for your help. I have worked through the various items you have mentioned above, rebooting each time after making any changes. Nothing has worked, sadly.
On item 7 above, I got an error message after entering the following information:
net use S: \192.168.1.1(disk name)
I put the actual disk name in the above.
The error message was: System error 3227320323 has occurred
I don't know what to try next.
EDIT: I looked up the error code and found some useful information. It suggested disabling the SMB signing by use of the command (in the powershell):
Set-SmbClientConfiguration -RequireSecuritySignature $false
Having done this, I rebooted and hey presto I can now see the NAS disk.