Select proper boot device. help ;-;

[truehug]

Context

SO, I just built my friend a new pc. Everything is new but his case and hard drive are from his old pc. He had windows 7 previously, which I planned to update to windows 10, however it had some issue where the mouse and keyboard wouldn't work in windows 7. Anyways, that issue has been fixed. I did this by putting his hard drive into my PC and copying his user area then formatting the hard drive, switching it to GPT, since windows said it couldn't be installed on to MBR. Then I successfully installed windows 10 and all was fine. 

 

Issue

The issue is, when he installed the hard drive into his system, he couldn't boot to it. Gets a message along the lines of select proper boot device or install boot media into selected boot option. His Hard drive does show in bios.

 

What I've Tried

I have messed around with CSM, switching legacy on and off. I've disabled secure boot, fast boot. Just not sure why it doesn't work when it boots fine in my PC. I think maybe something to do with it being within Windows Boot Manager when it was in mine, maybe? idk.

 

Specs in case that matters

My friend's PC has:

Ryzen 3 3300x

Asus Prime B450

16GB (2x8GB) Corsair Vengeance

GTX 1660 Super