Windows 7 Cannot format my PC

[paddypower]

system specs: PC, win 10 Home installed, (upgraded from Win 7. 64 bit OS, x64-based processor. version 1803 OS Build 17134.765.
problem: Win 10 failed; unable to open Defender. Plus, unable to connect to Internet (fibre optic cable is hard-cabled in to the box.)
I have backed up all of my data and apps. Instructions are to insert Win 7 into my CD drive. shut down PC. Restart. I did not get a request to strike any key etc. error message 'Win could not retrieve info about this disk on this computer'. any advice, please? (Off topic: as my beloved Surface tablet is going through meltdown (screen burnout due to over-heating).
''the horror'', etc,

 

[livix07]

If I were you I would retrieve the Product Key (assuming you have a genuine Windows licence) and do a clean install of Windows 10.

1) Please follow this tutorial to retrieve the product key:
Find Windows product key on all versions

2) Download the official Windows 10 ISO from here:
Download Windows 10 Disc Image (ISO File)

I highly recommend that you DON'T GO BACK TO WINDOWS 7 because it will reach the end of life next year:
https://support.microsoft.com/en-us/help/4057281