HI bigiba,
You can test the unit by connecting separate power lines to the unit from your computer’s power supply. Make sure that nothing else is connected using the same power line that you are attaching to the unit.
Also try to testing the unit with two hard drive inserted only.If it works then try 3 at a time, 4 at a time, 5 at a time.This will help us determine is this is a power issue.