diskpart
DISKPART> list disk → disk 4 as in the disk management GUI from computer management

mbr2gpt /validate /disk:4 /allowFullOS
→ OK

mbr2gpt /convert /disk:4 /allowFullOS

diskpart
DISKPART> select disk 4
DISKPART> list partition
DISKPART> select partition 2 (the one with the system)
DISKPART> active (set as bootable partition)
DISKPART> exit

bcdboot c:\windows