mashranga, If your player is detected as a ADFU Device it is in Recovery Mode and will still be recognised by MP3 Player Upgrade Tool but your player will not accept your backup dump.bin you will need to load a full version firmware then you will be able to reload your dump file.
The full version firmware does not have to be the exact one for your player, you will find some full version firmware
HERE. After you upload the fill firmware your player will be detected by windows and appear in explorer, you should format it before uploading your backup.