GPT Partition Style preventing Windows 10 Installation

I just built a custom pc with a new mobo.
The hdd is used and has 8.1 on it which is not legal on this mobo.

I can't really afford to buy 8.1 again. Especially since 10 is free.
I burnt 10 to a disk and when I try doing a clean install I get a problem with GPT message
"Can't install Windows on this disk. The disk is in the GPT partition style.".

I had no problem installing 10 on a laptop with 7. But that was a direct install from Windows, not a disk. 7 is a legal copy on that laptop and is still there for me to go back to if I don't like 10

I do like 10 and 8.1 on this mobo is not a legal copy so I can't legally upgrade it. Just a clean install of the free Windows 10 without ties to Windows 8.1.

Have you got your new motherboards Bios set to UEFI or Legacy BIOS?

Windows can only install to GPT when using an EFI bios, and booting from EFI media in EFI mode.

Having said this, you do understand that Windows 10 isn't "free". It's currently a preview version that has a number of problems, including compatibility issues, and issues which can cause you to lose all data or even potentially hardware attached to your system (there were reports of earlier versions of 10 bricking hard drives, for instance).

Further, once Windows 10 is released, it will only be free to those who have an existing valid Windows 7 or Windows 8.x license for that computer.

Further, once Windows 10 is released, it will only be free to those who have an existing valid Windows 7 or Windows 8.x license for that computer.

I knew I read something about Windows 10 being FREE for the Technical Preview Users & Testers. I know my eyes can be playing tricks on me because I really want a totally free copy of 10. BUT,, after reading this article by Paul Thurrott many times; I believe it says anyone can UPGRADE to Windows 10 from 7, 8, 8.1 or Windows 10 Technical Preview. I could be wrong again.

I've tried with UEFI Enabled and Disabled.

I think mobo is set to UEFI

This is what appears in one of the sections for UEFI or BIOS

Boot Option Priorities
AHCI PO:WDC WD10EZEX-602F5A0
AHCI PO:Optiarc DVD+/ AD72
Windows Boot Manager
UEFI: Optiarc DVD+/ AD7200S
Disabled

choose custom install and delete all partitions and let the windows installer format and partition for you.

Edit: like Mystere said, to use Windows 10's RTM you're going to have to get an activation key be it 7 or 8 or 10 when the preview phase is over. The only legal free OS's are some linux distros.

I'll need to get another hdd for backup before I delete all my partitions and data.
This article goes with the first one I mentioned and provides the key about halfway down.
My reading comprehension isn't the best and I know it. There was another article I'm looking for where, MS is treating all versions above Vista as "Eligible for Windows 10 Upgrade" . "Windows 10 Technical Preview" included

I've tried with UEFI Enabled and Disabled.

I think mobo is set to UEFI

This is what appears in one of the sections for UEFI or BIOS

Boot Option Priorities
AHCI PO:WDC WD10EZEX-602F5A0
AHCI PO:Optiarc DVD+/ AD72
Windows Boot Manager
UEFI: Optiarc DVD+/ AD7200S
Disabled

You need to boot from the UEFI: Optiarc DVD+ to boot in UEFI mode to install in UEFI mode.

Thank you. I'll be back to let you know.

choose custom install and delete all partitions that part worked ok
and this second part never appearedand let the windows installer format and partition for you.

Edit: like Mystere said, to use Windows 10's RTM you're going to have to get an activation key be it 7 or 8 or 10 when the preview phase is over. The only legal free OS's are some linux distros.

it said something about partitions not being in right order and I clicked Next anyway. No more illegal 8.1
Oh well, I have a clean hdd even tho I may need to buy a new one and reinstall 10