Hi DayLightMisery,
Unless you have done something rather serious to the Ethernet port, I doubt you have broken it. It is more than likely missing the MAC address and/or it has not properly connected to your network.
To do so, first start the MFDeploy application:
1. Go to the Start Menu > Programs > Microsoft .NET Micro Framework 4.2 > Tools
2. Run MFDeploy.exe. Be careful to run MFDeploy.exe and not MFDeploy.exe.config (as file extensions are hidden by default)
Then to set your MAC address:
a. Start your Netduino Plus in TinyBooter mode by holding the pushbutton while plugging it into your PC using a MicroUSB cable.
b. Select the Target > Configuration > Networking menu. Re-enter your IP address settings and MAC address.
c. Detach and reattach your Netduino Plus (power cycle)
Hopefully this helps.
Cheers,
Steve