I recently found this info useful from this link, when I was repurposing an old disk for a temporary and experimental installation of windows.
To manually wipe a drive and convert it to GPT:
- Turn off the PC, and put in the Windows installation DVD or USB key.
Boot the PC to the DVD or USB key in UEFI mode. For more info, see Boot to UEFI Mode or Legacy BIOS mode.
- From inside Windows Setup, press Shift+F10 to open a command prompt window.
- Open the diskpart tool:
- Identify the drive to reformat:
- Select the drive, and reformat it:
select disk <disk number> clean convert gpt exit
- Close the command prompt window.
- Continue the Windows Setup installation.When choosing an installation type, select Custom. The drive will appear as a single area of unallocated space.Select the unallocated space and click Next. Windows begins the installation.