Urgent: No monitor output after disabling safe boot

[TyMB43]

I recently bought a new hard drive for my Pavilion desktop, and was trying to figure out a way to transfer windows 10 to it. I created a system image on an external hard drive so I could get it on the new hard drive. I went into bios and switched around the boot order, making the USB hard drive boot first. I then tried booting several times with no response other than a screen telling me there is no OS installed on my hard drive. After this, I followed some online instructions telling me to disable secure boot and enable legacy boot. I did this, and now every time I power up the computer there is no monitor output. I really need this computer for work so some fast help would be greatly appreciated. Thanks.

[Hibb1]

Is your HP a tower unit (possibly white front) with an add-in AMD graphics card? I remember having this issue a few years ago when replacing the mainboard in these units. Yes - for some reason when you changed the secure boot setting, it no longer booted off the AMD card.

My solution at the time was to remove the AMD card and connected the screen to the integrated video out. then change the secure boot setting back.

You could also try removing the CMOS CR2032 battery for 2-3mins and see if when BIOS goes back to default, it's the right setting. I *believe* that updating to the latest BIOS version fixes this issue. Just don't update through the HP Support Assistant. There's a good chance you'll brick the unit if you do. Just download the executable file from the hp drivers/downloads section and run it manually.
In relation to your original task, probably the easiest way would be to create a Hirens PE bootable USB stick and clone your old drive to the new one. Or create a Windows 10 USB from the microsoft site and install a clean Windows 10 on the new drive and manually migrate the data you want once its done.