Only can connect wired if connected wirelless first

Please,

Since about october last year I can no longer get my MacMini connect directly to wired LAN. First I need to connect wirelessly and even making my airport inactive (off) the wired LAN remains working after doing so.

If I startup the MacMini only wired connected to LAN, system preferences says that computer is connected but internet is not available. To make it works, then I need to activate airport...so it begins working (again if I inactivate airport, the LAN remains now available to the internet).

I have tried many things including reinstall Mac OS X SL combo update with out any success.

Any suggestion is welcome.

Lab Zen