Hi all!!!!

I had an isight webcam which fell and hit the ground then no longer worked. I then purchased a Logitech HD webcam C615 which indicated it is Mac compatible. Installed using the disc provided and plugged it into an open usb port. (Would not fit into port where the isight use to plug in). Everything works great except for when I use it with Yahoo Messenger for video calling. The person on the other end can see and hear me but I can only hear them......I cannot see them????? When they try to invite me to view them, a pop up comes up and states that it appears that my configuration is not compatible in order to view them???? I downloaded macam thinking it would help but when I click on the macam icon it states I have no camera hooked up????? I have an IMac G4 20" flat screen PowerPC (sphere type) running Leopard version 10.5.8 and using TenFourFox as my browser. Any help on this issue would be greatly appreciated!!!!!!!!!!