Thank you for replying me! Ok, I've followed all of your suggestions... Cleaned the dust using vacuum cleaner, even in the ram bay... Done SMC Reset...
But my Mac crashed 5 minutes ago... This is an extract from kernel.log:
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `CodeResources': 93
Jul 1 15:23:41: --- last message repeated 1 time ---
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `Headers': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `Resources': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `Current': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `CodeResources': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `Headers': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `Resources': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `fr_CA.lproj': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `pt.lproj': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `Current': 93
Jul 1 15:23:41 imac kernel[0]: CoreServicesUIAg[1623] Unable to clear quarantine `CodeResources': 93
Jul 1 16:01:26 imac kernel[0]: NVDA(OpenGL): Channel exception! exception type = 0xd = GR: SW Notify Error
Jul 1 16:01:26 imac kernel[0]: 0000006e
Jul 1 16:01:26 imac kernel[0]: 00200000 00008297 00000474 00000010
Jul 1 16:01:26 imac kernel[0]: 0000047e 00001458 0001c801 0000000a
Jul 1 16:01:26 imac kernel[0]: 00000000 00000000 00000013
Jul 1 16:01:26 imac kernel[0]: 00000010 00000000
My gpu temp was 54 degrees... **** it, I was simply surfing the web... Not advanced graphics renders, no video editing... No gaming... Just surfing the web...
Can Apple change this faulty Mac?