My computer is few months old, 1GB RAM intel duo core 2.80GHz. It have been a great computer to play games for the first 4months then all of a sudden, while playing Roller Coaster Tycoon 3, the screen will hang suddenly. The computer just hang with the last scene before it hangs without any lags before hanging. Weeks later, Age of Empire 3 and Warcraft Frozen Throne also starts having this problem. And slowly, all the game I've been playing hangs while playing.

I've cleaned all the Fan of the CPU and took off the side panels of it. It still hang. And the Colour bit is right. FanSpeed shows that my CPU is 46C+
System is 33C+
Core is 42C+
Temp1 is 54C+
AUX is 46C+
HD0 is 34C+

Please tell me what is happening to my CPU.

Well, have you filled your PC up with lots of junk?? If so, running apps (in the tray etc) can slow it down, causing hangs and/or lag. Try getting rid of stuff you dont use .Also, try download eusing free registry cleaner. It deletes old dead entries, making your computer go faster. I found that crashday runs much better after i've just cleaned the registry.