Last attempt before get brick I 'd try download new firmware and schedule to reboot (install after reboot) it.

Now my Routerboard get a beeping loop and ether 4 LED solid (No cable connect on ether 4) before beep sound and reboot again and again.

I try to use netinstall plug LAN cable from PC to eth1 (POE in) and press reset for 15 seconds 'til ACT LED off after blink.
and then nothing show on netinstall screen, after that it reboot with beep again.

how can I fix it

Thank you.
PS. sorry for my english.

Hello,

try to netinstall again, we've had few 751s and 951s from customers showing the same behaviour.
Every unit was recoverable via netinstall and works flawlessly since then

greets