As per the error, the disk where you want to set its partition as active is likely to be formatted in GPT (GUID partition table) instead of MBR disk.
On a MBR disk, the system partition must be configured as active partition. Generally, the activate partition is set as the bootable partition which holds the operating system, and only one partition on each disk can be marked as active or bootable.
The ACTIVE command can only be used on fixed MBR disks.' is likely to appear when you attempt to mark a partition as active using DiskPart. The error 'The selected disk in not a fixed MBR disk. My questions: how do I make boot partition active or make computer boot as before?' It seemed that the making partition as active command was not available, as it ended up with an error saying the specified disk is not MBR formatted. I tried repairing master boot record via command bootrec /RebuildBcd, bootrec /fixMbr, bootrec /fixboot, active, etc. There seemed to be a system update while the computer was able to boot for the last time. I get the BSOD error 'Invalid partition table', and the computer won't boot. 'Hi, I've been having trouble booting my computer.
