repair windows sve14a2m1rw

Hello! I will explain the situation, then I will ask a question. On my laptop sony vaio sve14a2m1rw there was a licensed windows 8. I decided to upgrade to windows 10. The laptop began to work incorrectly with the new system and I decided to return the old OS. When trying to return the OS back through the restore function in the system, the computer freezes. I tried to do a full disk cleanup through the standard boot menu. Cleaning is stuck tight by 2%. As a result, I got a semi-formatted disk with untouched hidden partitions. And as I assume with the modified mbr. Most likely, windows 10 replaced mbr, so the system could not be restored. When I bought a laptop, I immediately created recovery discs. There are 4 dvd's. When I try to recover from them, the system still sends me to windows 10 and the standard recovery menu. Now questions.
1. I suppose that hidden partitions do not allow me to recover from disks. If I delete them and reformat the disk, can I recover from the disks?
2. I read somewhere that the key from the Windows included in the kit is sewn into the BIOS of the laptop. Is it so?
3. If my options are incorrect, how can I restore the OS?
PS I changed the boot from the disk to the BIOS and set the parameters for loading through third-party bootloaders (I don't remember what they are called, but I googled on them).