A "PXE-E61: media test failure" is strictly informational and does not stop a machine from booting or being used. Your issue is somewhere else.
I just got a older computer for my kids to play with. Its a 480. Every thing worked fine until I went to install a new video card and I get a PXE-E61: media test failure, check cable error. I reinstalled the old card but get the same error. I have no clue what this is or how to fix it. Anyone who has any idea or can help in any way I would be greatful.