Followed this to convert OS drive to GPT, it's pretty painless doing it via Windows RE:
https://www.windowscentral.com/how-convert-mbr-disk-gpt-move-bios-uefi-windows-10
I was gonna do it by booting from a Windows 10 disk (recovery tools), but my install DVD doesn't boot anymore... then I found out the latest Win 10 build doesn't even fit on a rewritable DVD
https://www.windowscentral.com/how-convert-mbr-disk-gpt-move-bios-uefi-windows-10
I was gonna do it by booting from a Windows 10 disk (recovery tools), but my install DVD doesn't boot anymore... then I found out the latest Win 10 build doesn't even fit on a rewritable DVD