Last night my 24 inch IMAC seized up. Restarted and for the next 10 reboots had no screen, just the looping BONG sound every 5 seconds. Tried a few suggested key commands at start up. Screen would flicker like a strobe light with some horizontal banding. More reboots and eventually got to the desktop. Now that the Mac has sat overnight it will start up, but shortly after gets static-like garbled pixels and freezes up altogether. The visual problem can best be described as static, not banding, not lines, just scattered visual static dirt and broken graphics. Any advice? I miss my computer already and will have to take her in soon. Thanks for any info in advance.