My work iMac is having serious problems at start up, but the symptoms keep changing, so I'm not sure what the culprit is. Friday, I turned it on from sleep and it didn't wake up. Held down the power button to do a restart. After the startup chime, I got several beeps, suggesting a RAM problem. Restarted again, same result. Tried again and it went past the apple logo, then dropped to black and sounded like the optical drive was spinning up repeatedly. After power down/up it would do this behavior: black screen, drive spin up sound, pause, drive spin up sound. That's where I left it and returned today. Power up gave the same black screen, drive spin up routine. Tried again and it immediate gave the startup chime and Apple logo, then white screen with cursor, which switched to spinning beach ball, then froze. Next start up with chime and logo all the way to the desktop. The computer is clearly unstable, but I'm not sure where to approach a fix. Thanks.