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#21
Whilst not related to this Windows 10 forum, I had major problems using a UEFI Windows 7 USB boot disk.
The initial installation worked perfectly on my standalone HD allowing me to install updates & applications until I added my MBR Data HDs. The new build was then not recognised with the following error message: 'Reboot & Select proper Boot device or insert Boot Media in selected Boot deice & press a key'.
It was still not recognised even after I had removed all the MBR HDs & I could see no obvious way to repair the build other than a re-install which replicated the problem.
Converting the GPT HD to MBR & re-installing Windows 7 created a situation where files were coped to the HD but on the first re-boot, the same error message was repeated.
Even cloning a working Windows 7 build to this HD resulted in the same error.
I used AOMEI Partition Assistant & then Diskpart/Clean to initialise the HD but no success.
I then used the Windows installation DVD & to my surprise the installation was a success.
No idea what was going on because previously that HD had a build of Windows 8.1 on GPT partition which worked OK; even restoring that build back to the HD failed.
Can only conclude that are problems if you have a mix of GPT & MBR HDs with OS on them.