So I bought an PC/LAPTOP VGA SVGA TO S-Video 3 RCA Composite AV TV Out Converter Adapter Cable to play my GameCube on my Monitor but I can figure out how to Switch it? This is where I got the Cable. http://www.ebay.com/itm/351233132129?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
The cable you bought it meant to work in the other direction. It's supposed to convert a VGA video signal output from a PC into composite (or S-Video) video output that you can connect to a TV. In other words it would allow you to connect your desktop PC to a TV.
You need a converter that will convert composite video (or maybe S-Video if you have an S-Video cable for your GameCube) to VGA, HDMI or DVI depending on what inputs your monitor has available.
That cable you have is not going to work with your GameCube. You can not convert passively an RCA output to an VGA. You need some sort of converter box (active!)
Something like: Link in Amazon.com