if you have a g5, i would not try to run the system anymore… you may have a coolant leak and any attempts to continue usage of the system may cause a lot more damage. apple will replace the cpu’s for free, but they will probably not replace any damaged ram, power supply or mother board without a really good sob-story. unplug and open the tower, look at the bottom of the tower, just above the power supply. see if there is any brownish crusty residue around there. if so, then you have a coolant leak, and will need to take it to a apple authorized service place. like i said, the cpus should be replcaed for free, any further damage may cost you… i think a power supply runs about $800, and the mother board isn’t worth replacing, at that point get a new mac (or tell them you’ll never buy a mac again if the can’t help you out… i have heard of people getting new macpros when their g5 died from a coolant leak).
if you don’t have a g5, i would run the apple hardware test… it should be on the osx install disc that came with your mac. there should be some instructions on how to load it printed on the disc’s face, but usually you’ll insert the disc, reboot and hold the ‘d’ key (some times the option key, then select the hardware test icon).
once it’s up, choose to run the more extensive test to fully test your ram and video card… this test should take while. like tom and brian, i’m leaning towards a video card issue…
if hardware test doesn’t find anything, run the disk utility from the install disk — reboot with disk in, hold ‘c’ key, then once the top menu bar becomes active you’ll choose to run the disk utility from one of the menu choices (it may be ‘utilities’ but i can’t remember). select the boot drive and choose to repair disk.
if things are still not working, remove any third-party pci hardware like video capture cards (decklink, aja, etc.) or sata host adapters. i’d even disconnect any usb and firewire hardware other than the keyboard and mouse.
after that, i guess you’re headed to the genius bar (or other apple certified service provider).
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW