Unless you have bootmii/boot2 you are stuffed. Your Wiikey2 won't help you recover this one. I believe this is an IOS50 stub brick, seen lots and lots of these where people have gone from 4.0/4.1 to 3.2 and back up to 3.4 via disc.
I'm assuming you didn't install IOS50 v4889 when you downgraded which would have saved your Wii.
Bin or Repair.