Hi. I recently got a imac g4 off of ebay. For the past week or so, every time the computer runs for over 2 hrs. it either freezes or a strange message comes up on the screen that tells me i need to restart the computer by holding down the power button. Before this happens, the graphics do very strange things and then freeze. Is it a logic board problem, or something else? If so, can i get a new logic board that is faster than the one i have now? (i got 700 mghz...slow i know, but it was a good price...i wonder why?!?!?!)