iMac G5 Isight 20in 2.1ghz Display Distorted

iMac G5 20" iSight 2.1ghz A1145

Hello,

I am a new Mac user that acquired a G5 iSight 20" 2.1ghz. The computer start just fine and has a normal display screen for about 10 to 20 minutes. After 10 to 20 minutes the video gets distorted and nothing is clickable with the mouse. Eventualy the mouse icon changes to a turning rainbow wheel of some kind. As I said; I am completely new to Mac and do not even know anything about the operating system. Does anyone have any ideas on what can the problem might be? I am worried that it is the logic board. Is it possible that the drivers or OS is corrupted?