DNX 5240bt loading and updating gps loop...

Hello everyone.

I tried to update dnx5240bt firmware to 2.80.At 27% of the procedure suddenly the unit restarts and after that keeps restarting the nav and says "loading" - "updating".
I cannot see the unit with usb because of the restarts.I see it for a few seconds and then disconnecting.
Can you please help me?

Thanks in advance