No drives available while booting

[NiKiZe]

Are you using the default boot.wim? have you pressed Shift+F10, mounted the NAS and started setup.exe from there? (what you see can be due to that install.wim is not found)

the mount command is something like
net mount * \\nasname\share
this will mount a driver letter that you can go to and start setup.exe (in the same path as you install.wim) "again" and hopefully that will work.