I think you have a defective cable.
As when I made the switch over, I was able to access the wii settings after installing the component cables. Or you have not properly installed the component cables. Lastly when installing a different input connection you have to set your tv to that new input connection when in use. (Example your cable box connection may be input 1 while your wii component connection may be input 3). The input ports are usually labeled on the tv at each input port.