The V2.00 firmware had a bug which can cause power up hang problem after the firmware upgrade.
If the first empty space in the HDD is not continuous 512KB, it can have this problem.
To solve the problem, you need to take out the internal HDD from ND2730 and format the drive at the computer using another USB case, then add the HDD into ND2730 again. Then you'll be able to use it.
Sorry for this problem.