Help with changing active partition  

Now, for the record, I have two drives with active partitions as well but one is an external drive. I also have a different partition structure as shown below:

@aardvark
FYI, you don't have 2 drives with active partitions.
If you install Windows with GPT partition scheme. Your Boot partition is 100MB EFI System formatted as FAT32, where your BCD (Boot Configuration Data) resides in. There's no such thing as Active partition with GPT disk. EFI firmware looks for the EFI System to boot from.

Active partition can only be marked as Active if your disk is initialized with MBR. With GPT disk, if you try to mark "Active" on any partition with diskpart, you would get an error.

Having said that. Your Windows was installed using GPT partition scheme, your Z drive is a MBR disk and if it is a data disk then it should not be marked as "Active". However, If your Z drive contains another OS and is MBR then it must be marked as Active in order to boot from.
Here's an example, Windows 10 was installed on Disk 0 with GPT scheme. Windows 7 was installed on disk 1 with MBR so it must be marked as Active on the System Reserved partition. This configuration is not dual boot. In order to boot Windows 7, I must change the boot order in the BIOS or use the Boot Menu for one time boot. Hope this helps !!!

aardvark said:

@topgundcp: Thanks for flexing your technical prowess but I still maintain that I have an active partition. It doesn't actually have to say active to be active. So, I don't want to play on words here and I will provide a link to a developer (who you always make reference to as your hero of sorts) where he sums it all up in a simple sentence:

Win 10 no active partition - Windows 10 Forums

@aardvark
I am sorry but I'd never reference any body as my hero, I'd praise him if his answer is correct. However, in this case, he's dead wrong by saying it as Active. The correct answer was the post after his by genet:
Win 10 no active partition - Windows 10 Forums
The Boot process on a GPT disk is controlled by the EFI firmware ie. Windows Boot Manager. Period.

Or just delete the drive to unallocated space during the install.

Unplug ALL other drives.

1. The drive started by having undeletable partitions. I seemed to have fixed that by doing the appropriate steps in diskpart.
2. I know the terms MBR and GPT and have even heard of UEFI and EFI, but not CSM. However that is the limit of my familiarity with them.
3. The PC from which I cloned the O/S, and in which I want to test whether cloning was successful, does NOT allow for hot-plugging of HDDs, so I suspect that makes it a legacy PC. The 1TB HDD is destined to run in a not-new laptop.
4. I did the exact same procedure to a 80Gb SATA HDD, and I could mark the partition as active, and it did boot that legacy PC.
5 Where/how do I find the option to convert a GPS to an MBR partitioning system ?
6.I have NO intention of re-installing the O/S