Strange IMac 27" crash –need help

I am having the iMac 27" was playing left 4 dead and then unexpectedly it totally crashed. I was somewhat shocked by this as I have had it devoid of locking it up otherwise something yet. There is just the one thing that I can think and that is about a week ago. I have upgraded the RAM to the 16gb so it may be because of that but there is one confusion that how does it was running till now without any problem. Other than this, when I reboot then I can see that there is a little spinning circle loading bit which is loading a screen that is partially grey distortion and after that it turns to black and white squares. Please help me friends.

This is seemed to be problem because of the bad Steam software. So it will be helpful to you if you can uninstall that and install it gain. See if this helps you.

Uninstalling the Steam software is good idea and there are more chances that this will resolve the problem for you. But if after doing this also the problem is not getting resolved then you can simply repair disk permissions and after that you will have to scrap all the plists associated with the program. This can resolve the problem for you. This is the only thing that I can suggest you for the time and I hope that it will be helpful for you.

Is that unit is still under warranty? I am asking this because if this is under the warranty period then just take this to the dealer of this and ask them about this. Otherwise you can directly contact to the Apple support and they will help you with that. This will be the best option for you.