Do you mean, if you run the Nuendo and your project off your boot drive everything works, but if you run Nuendo of the boot drive and the project off another drive then it does not work ???
If this is the case, I would be suspicious about the project drive or the computer port it is connected to.
If this were a windows-7 or earlier I would ask you to check the bios settings. Can you actually check bios in Win-8 ? I saw somewhere that Win-8 uses a different scheme (depending upon the manufacturer).
Also could the drive be going into standby because of the power settings ???
Are there any permissions issues with using another drive on your system ???
Keep us informed, hopefully we can get this figured out.
Later,
Brain