When I do that I get "Error loading operating system" again. WTF? So, anyone know how I can fix this because right now I have a computer whose only function is BIOS ...

To fix Operating System Loader has no signature, Incompatible with SecureBoot, All bootable devices failed Secure Boot verification error, follow these steps.

My main rig; P4P800/P4 2400 has been running strong for the past few months, with the replacement of it's normal IDE HDDs to a shiny new Seagate Barracuda V about a month and a half ago ...

While booting a Hyper-V virtual machine, if you get No operating system was loaded error, this guide will help you fix the issue.