I have vertical lines showing up on my 2.16 GHz 2 GB RAM Core 2 Duo iMac. Any idea what's going on and what I need to do to fix it? My computer is also freezing frequently.
It could be either a driver issue or a hardware problem. If you are still under AppleCare, I would just take it to a Genius Bar so they can do a diagnosis and see if it's a hardware problem (the easier fix). Otherwise, I'd recommend doing a full backup and installing a fresh copy of OSX.