If the screen stays black,
it means you have successfully entered Dfu mode.
If the screen stays black,
it means that you have successfully entered Dfu mode.
If the screen stays black afterwards,
it means that you have successfully entered Dfu mode.
Fone will ask you to follow the on-screen instructions to set your phone into the Dfu mode.
If the phone screen is still black
at this point, then you have successfully entered the Dfu mode.
Fix for(some) USB dongles that are stuck in Dfu mode after a firmware update(including the D-Link
DBT-120 rev B3).
I have done hard
reset, backed up from old backups, even done the Dfu restore and set up as a new phone.
Note: If the iPad or iPhone does not appear in iTunes, put it into Dfu mode first and then restore as usual.
If you see the Plug into iTunes screen,
it means you haven't entered Dfu mode and that you will need to start all over again.