I have a 750RB work fine for 1 year..

I tried to reset it to factory default setting by holding the reset button and power cycle it. The ACT flashed and then off. After that I release the reset button.

However, after that, I cannot go into the configuration via Winbox anymore. The ACT LED is always off (even after I power cycle it again).

The strange thing is that 750RB can still give me IP address 192.168.88.254 / 24 with gateway 192.168.88.1. But I cannot ping 192.168.88.1 or access via winbox. The ACT LED is still always OFF.

I try to netinstall via Ethernet port 1. But netinstall cannot detect the 750RB.

try another ethernet port for open with winbox.

Try all ports already

Something like that happend with me but there is no ethernet connection after resetting the board, can't login. Going crazy

Are you using Winbox? If so, start Winbox and next to the "Connect to" box there is a button with "...". Click on that and wait a couple seconds. Your router should appear there, even if no ip is assigned to the port. It may show only the mac address.

SurferTim, winbox is not showing any MAC or IP maybe because the ethernet ports are not even blinking/connected or working(all 5 ports).

Sounds like a good candidate for netinstall

Yes indeed, try with netinstall procedure like here
http://www.wirelessinfo.be/index.php/mi ... etinstalle