LAN CARD (network adopter) doesent appear

i have DELL LATITUDE D600 LAPTOP it has both wifi and built in LAN CARD when i turn on my laptop ..the wireless network card works fine but windoes does'nt detect othen LAN CARD even windoes cant find in new hard wear search...but some time when i turn my laptop on  both lancards work fine.... can anyone tell me whats going on here.?