I am sorry, but I tried what you said, but still the same result. I think it is something to do with the Bootstrap. The Dell is UEFI, and my laptop is MBR. So the Boot on the flash drive is MBR, but MBR is what loads Windows 10. The Dell is, on restarting,  looking for UEFI Boot, cannot find one so comes out with an error.   Thank You for the Help, grahambl 
I was given a Dell Inspiron 3671 desktop, without a primary drive. I had a 512Gb SSD, which I added. Windows 10 was installed OK, but when it restarted I cannot get passed the "No Bootable Device Found".  Can anyone help, I am a pensioner with very little money.  
I have been given a Dell Inspiron 3671 desktop, without any primary drive.