G
Have a logitech web cam worked great for a while then just stopped working. Now when you click on the yahoo messenger open web cam it frezzes up and have to restart to get it to unfreeze. 
Web cam problem
dude
try this
when ever its freezed, goto standby mode & again comeback to normal mode. Now try your webcam in yahoo/msn. If this is resolved den your usb has some (technical) power supply issue...