Failed attempts to repair GPT partition table

My failed attempts https://youtu.be/iGYKff3MZAE and http://goo.gl/7ryCx3

GPT and MBR disks can coexist. But you only can boot from MBR, if your UEFI firmware aka UEFI-BIOS has a Compatibility Support Mode. UEFI and MBR installations cannot be mixed on each disk. If you change your second disk to GPT and add an UEFI ESP, your Windows on it won’t boot. The change is made when you save the partition table with gdisk. The data will be kept, but any installation won’'t boot.

AFAIK, any Linux installer will use the existing ESP or create one. No need to create an ESP manually. That is clearly something a program should do.

Best regards,
Bequimão

Thanks, I will try to learn about gdisk!

My motherboard firmware has what it calls “Legacy” boot mode. I was thinking of keeping my second disk as MBR but changing the Windows 10 partition and two Linux partitions to UEFI mode according to this link http://askubuntu.com/questions/447686/how-to-boot-windows-8-from-a-legacy-mbr-partition-in-uefi-mode-via-grub

I do not recommend to activate Legacy mode. Please give valid information here in this thread. I am not willing to follow links to gather information.

I second this. Most here will not follow all sorts of links to third party web sites. You are also prone of being accused to introduce spam in the forums.

BTW, I see you are rather new here, thus allow me to introduce you to the way copied/pasted computer terminal output should be posted.
Please in the future use CODE tags around copied/pasted computer text in a post. It is the # button in the tool bar of the post editor. When applicable copy/paste complete, that is including the prompt, the command, the output and the next prompt.