External harddisk won't boot anymore

I have an external harddrive with 2 partitions:

• one for mass storage and backup (4 tb)
• one for booting windows installations, macrium reflect and other media that needs to run from boot (8 gb)

The bootable partition I reused for various tasks, everytime I needed to use bootable media, I deleted the old files (not format, just delete) and extracted the new boot media to the root folder, but it doesn't work anymore. It won't boot anymore, it goes straight into windows.

I have no idea what I have done differently this time, but it bypasses boot on all my systems. I must have changed something, but I don't know what. How can I fix it?

It was working yesterday, on multiple systems. Then I ran Macrium off the external hard drive (in Windows) and a bit later I found out that the disk didn't boot anymore. Then I did what I always do: delete all files and extract one of my backups of a previous bootable disk. But still, no booting. So then I reformatted the 4gb partition with FAT32 and tried again. But still nothing.

I don't know is it of any help, but here is a picture of how it looks in the windows disk management. Disk 2 is the troublemaker.

A simple reason for skipping a boot from external media like a usb is that Windows had Fast Startup turned on when you shut it down.

Either turn it off, or when in Windows don't use Shut down, use Restart instead (which performs a full start up from cold).

Nope not it. I have tried fastboot on and off, and restart and shutdown both. But it is all the same. Also F12 on boot, specifically pointing to the external hard drive to boot from, is still going straight to windows. The problem is the hard disk layout, not bios or windows.

OK, had to eliminate the possibility.

Legacy bios or uefi? The Fat32 boot partition needs to be set as Active for a legacy boot. I note your Macrium (Q:) isn't active.

UEFI and I also just turned off secure boot, just to make sure.

But I am telling you, it worked before, nothing on the laptops' config has changed, the only thing that could have changed is the hard disk.

I tried to mark Q as active, but in the disk manager the option is greyed out. And through the command line and diskpart says it is not possible and gives me the following message: "The ACTIVE command can only be used on fixed MBR disks"

MightyMauz said:

... it worked before, nothing on the laptops' config has changed, the only thing that could have changed is the hard disk.

Then the finger of suspicion points to the files on the Fat32 partition. You said in the first post that...

MightyMauz said:

...I deleted the old files ... and extracted the new boot media to the root folder, but it doesn't work anymore.

...so logically the only thing that has just been changed are the files on the boot partition.

As an experiment, lets see if it will boot from a usb recovery drive on a memory stick. If you don't have one, you can make one. Untick the option to include system files, they're not needed for this test.
Create Recovery Drive in Windows 10

If it boots from that, try copying all the files and folder from the recovery drive to your HDD's Fat32 partition. Can you boot from that?

MightyMauz said:

I tried to mark Q as active, but in the disk manager the option is greyed out...

...as it is for my external bootable HDD. That's normal in Disk Management.

...And through the command line and diskpart says it is not possible and gives me the following message: "The ACTIVE command can only be used on fixed MBR disks"

...that's odd. I've just changed mine using Diskpart's INACTIVE command, than back again with the ACTIVE command. Mine's only a 1TB drive though, so it's using a standard MBR layout. I'm not sure if that applies in the case of your 4TB one.

I know that @NavyLCDR also uses a bootable external HDD, perhaps he has some ideas on what your problem is...