We had this exact issue but for M4 blade, finally what worked for us was "Uing the BIOS Recovery DIP Switch" from Cisco installation manual in Pgae 110. it literally says: "If the BIOS BootBlock is corrupted, you might see the system get stuck on the...

CSCux75436   WLC loses default kernel route when dynamic int is created on 2nd port This should get you back to your backup image (once you access the GUI you can upgrade again to 8.1) using serial cable, access the CLI config boot backupconfig wlan...