Converting MBR disk to GPT using cmd

I've converted my drive to GPT but when I partitioned the drive, at the point when I type in active it is giving me an error message saying

The selected disk is not a fixed MBR disk. The active command can only be used on fixed MBR disks

At first I ignored the statement and tried to install Windows 10 as it is I get the message saying

we couldn't create a new partition or locate an existing one, see the setup log files.

The active flag is only used in MBR where bootloaders are very simple (as they have to fit into the 446-byte space in the tiny boot sector) and uses that flag to load the OS in the active partition. It's clear from the error output

The selected disk is not a fixed MBR disk. The active command can only be used on fixed MBR disks

OTOH there's no concept of "active" disk on GPT. The boot order information is stored in UEFI flash and ESP. The ESP is also large so bootloaders can be complex and doesn't have to load the next stage in the EBR

You said that you converted the drive but what command did you use? If you used the built-in MBR2GPT.EXE then after the conversion the partitions should be the same as before, and if there isn't a free partition to install the new Windows then installation will fail