If "boot" stays on the front display it actually isn't starting/finishing booting. The clock should appear within a minute.
Time for an emergency flash procedure I am afraid. Frankly never carried one out with a Dune.
Firmware Recovery Procedure
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In case of firmware upgrade crash (e.g. the player is switched off during firmware upgrade), firmware recovery is possible in most cases.
Perform the following steps:
Put a firmware DFF file at the top level of a USB flash drive (preferably use exactly the same firmware version as was attempted to install during the failed upgrade).
Rename the firmware DFF file on the USB flash drive into "dune_firmware.dff".
Switch the player off (using the power button on the player).
Attach the USB flash drive with the "dune_firmware.dff" file to the player.
Switch the player on.
The player should detect the USB flash drive and automatically start firmware recovery procedure. You should see "RECOVER", "CHK 0", "CHK 1"... "CHK 99", "REC 0", "REC 1"... "REC 99", "OK", "EJECT STORAGE AND REBOOT" messages on the front panel of the player.
On an error, a message "ERR ..." is displayed on the front penal of the player. Possible error codes:
"ERR Ann", "ERR Bnn", "ERR Cnn": A problem with the "dune_firmware.dff" (the file is invalid/broken, the file corresponds to a wrong player model, the file can not be read from the USB drive, etc).
"ERR Dnn", "ERR Enn": A problem during data copying (e.g. the USB drive disconnected during data copying).
Detach the USB flash drive from the player, and delete the "dune_firmware.dff" file from it (do not attach the USB flash drive with this file to the player when you switch the player on, otherwise, the player will attempt to recover the firmware again).
Switch the player off and remove the USB stick (using the power button on the player).
Switch the player on. The recovered firmware should load in the usual way.