[X4U] Losing ethernet

[Jim Elmore]

I can connect to the internet with either a wireless connection or  
through an ethernet connection. Both go to the same router and into  
the same cable modem. Occasionally, with no warning and with no  
pattern, it seems the ethernet port disappears. I can change to a  
wireless connection and reestablish an internet connection. In  
Network preferences, there is no network status at all when ethernet  
is selected. Network diagnostics indicates that I am not connected to  
an ethernet cable. Restarting restores everything to normal. This is  
a MDD G4. Could this just be a software glitch, or perhaps a hardware  
failure? Are there any other diagnostic tools that might be helpful?  
Thanks for any help.