Unable to boot - error code 0xc0000225

I don't know what to say... the computer is certainly doing something odd.

Sorry if I have confused things, but to be clear,
The Kingston is not the USB with the boot media - it is the stick I used to save the screenshots to.
The SanDisk is the drive with the OS.
The boot media is on the Lexar stick.

I don't know why the Lexar is not showing up as Drive Y - there is no drive Y shown in File Explorer, just drive X. The Lexar is also not showing up on Disk Management - again, I do not know why.

I took a few more pics of Disk Management and File Explorer without the Kingston drive and the DVD drive empty. As you can see, there is no drive Y and I don't see the Lexar in Disk Management.

So Disk 1 (the SanDisk with the Windows 7 installation) shows an EFI system partition, but you say there are no active partitions shown. Is that part of the problem?

Okay - that makes a difference! I believe that was the problem - I now have the USB booted from a USB2 port.

DiskGenius seems to have identified problems with the GPT on the SanDisk. I haven't done anything yet - hoping you can let me know the best way to proceed.

Note: I imagine you can ignore the removable drives shown in Disk Management - they're all from a memory card reader.

Thanks so much - the repair worked! No obvious issues with the system as far as I can see.

Any idea what would cause such a problem? There were no issues when I shutdown the computer the other day, but the very next it didn't boot...

Not sure what happened...

I was getting some different messages when I launched Usb7ice, but was able to ignore them and copy the 17514x64v32 ISO to the USB stick. However, when I rebooted, the USB was not shown as an option in the Boot Menu.

I booted back into Windows and the light on USB stick started flashing continuously as though it were being written to or reading from. The graphics started slowing down and behaving a bit erratic. I was unable to eject the USB drive without shutting down the computer.

I used FAT32 as I did with the previous ISO.

I tried copying the 17514x64v32 ISO to the USB stick again - this time on my laptop with Windows 10. It copied without any issues.

Again, the USB did not show up in the Boot Menu of my Windows 7 machine when inserted into the USB3 port. I was still able to boot from a USB2 port and for what its worth, I opened DiskGenius and its now indicating the ESP partition on the SanDisk is damaged. Presumably this is still a problem? I'm still able to boot into Windows as well though, so I don't know what to think.