To solve the problem wire the flasher on the mobo , dump the nor, patch it to 3.55 and flash it back and finish the downgrade in factory service mode this could help. Console most likely had changed IDPS with multiman and went wrong.
Or you can try this as well:
1. Remove HDD from PS3 and turn power on.
2. You should get a message like no storage media or operating system, THEN with the power still on plug in the HDD that will not update.
3. Power off the PS3 by holding the button, however if this does not work use the main power switch on the back and just shut it down.
4. Turn main switch back on and/or press power on button.
5. It should now say file system needs restored, do that.
6. It may lock up instead of restarting at the end, so power it off as described above.
7. Restart in Safe Mode and select option 6 with USB firmware update.