Windows 10 clean install

Can convert it to Gpt by entering the repair section of the usb install drive before the install of windows and using the diskpart commands.

DiskPart

list disk

select disk #        <select the drive windows is to be installed onto>

clean                   <will clear all data and partitions>

convert gpt

example;

x:>diskpart

Microsoft DiskPart version 10.0.17134.1

Copyright (C) Microsoft Corporation.

On computer: T520

DISKPART> list disk

Disk ###  Status         Size     Free     Dyn  Gpt

  --------  -------------  -------  -------  ---  ---

  Disk 0    Online          476 GB    47 GB        *           

  Disk 1    Online          119 GB    11 GB        *

  Disk 2    Online           29 GB      0 B

  Disk 3    Online          115 GB      0 B

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> clean

DISKPART> convert gpt

exit

exit

If you can not complete the install without a Key, enter this one

VK7JG-NPHTM-C97JM-9MPGT-3V66T

But once it is activated, you should have no issues doing a clean install and it be activated.

If it never had EFI partitions, then they will not automatically be created to EFI install.

You have to create the EFI partition (FAT)

and the MR, WRE, OS partitions (NTFS)

Just because you set it to GPT EFI from BIOS, it does not magically create these partitions and proper formats for them.

If he upgraded from 7 to 10 and never changed MB then it will activate during install. You do not need the Key.

I would do a BIOS install. There is NO advantage to EFI install except you can use HDD's over 2.4TB in size. BIOS is the best way with less issues.

Its the delete key on mine

When you start your computer  there is an screen that shows the computer type, at the bottom of the screen there is a message of how to get to the BIOS.  It may be an f key or just enter. It can be  quick.