It seems that your switch has a hardware problem with some of its network interface controllers and probably needs replacing. Sorry to bring bad news but if a POST fails with an error such as this (PHY loopback failed) and does not go away even after completely turning off the switch, waiting for a couple of minutes and then plugging it back into power with all devices disconnected from it then it's time to replace it.
Best regards,
Peter
Learn, share, save
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.