Given that you are unable to reach a usable command line when you console directly in to the AP, I would recommend opening a support case to pursue the RMA. The technician you work with might have a few things they can try to fix the AP for you without needing to wait on the RMA process, but it does sound like you might need a replacement and you've covered the basic troubleshooting steps well. Please reference this post in the case you make so they can see your notes here as well.