Hi everyone. Hope you guys can help diagnose a problem I have with my iMac. It's an early 2008 24" imac with 3.06 Ghz processor and an NVIDIA Geforce 8800 GS 512 graphics card. After buying Empire: Total War I thought it best to upgrade the 2GB RAM to 4GB, and purchased 2x2GB sticks 800 Mhz 6400 DDR2 SDRAM. When they arrived I put them in and the system booted up normally. I could surf the net ok, but when it came to watching a video on youtube full screen, or playing a game, it would cope for 30secs-1min and then the spinning coloured wheel would show. I'd then hear noises that sound like a cd trying to eject then the system would hang. One of three things would then happen: - it would automatically reboot showing the multi-lingual startup message that the system was not shut down properly - a grey blank screen would appear and not change - the grey start up screen would appear with the Apple logo and spinning circle, which would then stop spinning and not change. If I manually rebooted I just get a black screen and can only hear the fans softly spinning. I've tried swapping the ram sticks but get the same as above. It will boot and work normally with either one of the 2GB ram sticks installed on it's own. It will also work normally with the original 2x1GB sticks installed again. I don't get the 3 beep warning at startup. Any thoughts on why this might be happening? Would the graphics card be the reason for this issue? I'm not sure if these are related but a few weeks ago I noticed that the brightness would randomly change from normal to half-brightness then back to normal. These would change every few minutes or so and isn't dependent on what programmes I have running. I've also recently noticed that the top and back of the imac is getting quite warm to the touch and now I don't leave the system running when not in use.