Mobo ethernet port shuts itself off intermittently?

The ethernet port on my mobo keeps shutting itself off. (also shuts off the green/yellow light that is on when the ethernet is active).

I have to manually reconnect the ethernet cable in order to reactivate my ethernet port.

P2D CPU
T43 Biostar Mobo
500Watt OCZ PSU
5770
4GB RAM
Vista64bit

Does anyone know what is wrong? Btw, I had crashed to a black screen before this happened.