...after 72 hours... how I can recover it?
There is not serial port.....
Ideas about or I must throw it in the trash?

netinstall and contact support.

In case you wish to boot the device from network, for example to use MikroTik Netinstall, hold the S301 button of the device
when starting it until it beeps and the LED light turns off and RB411R will look for Netinstall servers.