I have an early 2008 iMac (24", 2.8ghz Core2duo, ATI Radeon HD 2600 pro, Snow Leopard). A couple of weeks ago, my screen went completely black, for no apparent reason. The Mac was still running but because I couldn't see what I was doing anymore, I had to shut it down using the power button and then reboot it again. Everything was fine after that. The day before yesterday, I was browsing the web with Firefox and it happened again. Same thing yesterday, watching youtube clips in Firefox. Has anyone experienced this before ? Does this mean my videocard/display is going to die soon ? Should I start worrying ?