2007 iMac screen problem

Just had a call from my sister who said that her 17" white intel 2007 iMac (running Snow Leopard) which was working just fine suddenly started showing lines moving in all directions and then eventually froze with diamond and square shapes on the screen. She was using a monitor since the iMac had developed the dread colored line problem about five months ago but had been working fine since buying the monitor. I certainly have no idea what this is and was wondering if anyone had some thoughts as to what it could be (bad logic board, graphics card etc.) There on a pretty tight budget so a ballpark suggestion about what it could be and if it's repairable would help a lot. Thanks

 

thanks for the tip, by the way here is a picture of the screen.

 

Yea, thanks for the help. Talked to a very nice Apple authorized repair service here and he said the same. Minimum $600 repair so my sister's investment in a shiny new Mac mini was the way to go. Just need to remove the hard drive so I can throw this baby away. Seven years seemed like a good run.