[ubuntu] ubuntu graphics card problem

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http://ubuntuforums.org – Hey , I have ubuntu installed on my iMac model 8,1 and it randomly goes to sleep, sometimes when it gets out of sleep mode the screen goes light blue but you can still see the desktop apps and everything and it doesn't go back to normal untill I restart my computer. So my question is, is this because my graphics card isn't supperted. Is my graphics card even supported. iMac 8,1 graphics card ATI Radeon HD 2600 PRO processor Intel Core 2 Dou 2.80GHz (Hardware)