Does the issue persist? You are correct that in general this could be a power related issue. At least it looks like it, but it seems you have a pretty powerful PSU. If this is a power related issue, the hard drive should be working properly when other hard drive is disconnected. Have you tried that? Could you tell me what happens when you try to access the hard drive? Is it correctly recognized in Disk Management? I strongly recommend you to check the drive on another PC.
Hope this helps