PID is FF66
OK, your adfuUpdate.inf is correkt, one problem solved
I take out the battery and connect player to computer VIA usb.
Switch player on and computer detects ADFU device but NO hourglass on screen, screen is blank.
Why do you have to switch player on ?? Player has to stay with the Button turned OFF until upgrade has been done (I always had the best results doing so).
It is normal that there is no hourglass now, because your firmware is still corrup 
I open upgrade program 4.05 and it reads as follows:
"It is in recover state, and select the firmware file for recovering please!"
followed by a file selection box.
Next I select the firmware Version 3.
I click on "Recover Firmware". The screen lights up, the program goes through upgrade process and reads: "Upgrade is success, the program will exit!" I click OK and the program closes down.
Perfekt
The player remains with screen lit up until I switch it off. The screen will not turn off on its own even after a half hour or so.
That's because the player wasn't OFF during upgrade prozess !
When I turn the player back on with the battery inside and usb unplugged, the screen stays black, no hourglass, even if I leave it for ten minutes switched on.
Hmm, not so good. Normally, inserting the battery and turning him ON with the upside Button, should show the hourglass in about 1-3 seconds, and then the player comes alive in about 1-2 minutes after the hourglass
Could you please give it a try with the player switched OFF with the upside button
I am working right now on an memory reset topic, witch brought back my player a week ago from the dead
But first, try with the player turned completely OFF (Not the play/pause OFF method, but with the Upside Button)
Regards
Jim