I cannot do Netinstall on CCR1036. There is no message "Press any key within 2 seconds to enter setup"

I have used CCR1036 for almost a year. It kept rebooting every several minutes. Some people said, it infected with Script sys. Anyway, I could not do my daily work, so I went to its console using serial comm. in order to install a new firmware. After I powered it, I could not find the message “Press any key within 2 seconds to enter setup” . Could you please advice me how to do Netinstall?