Windows 7 system does not turn on after adding 8GB RAM

There is some issue with my system and I am not able to figure out the reason behind it. I was trying to upgrade the ram as I am facing performance problem in my system. I am not able to get flawless gaming output. The system lags a lot. So I bought a 8GB DDR3 ram stick from Kingston. And I added that in the system. The pc does not work well at all. The system just fails to turn off. I tried a lot to turn it on but it is not responding. I am having a Gigbayte Z 77X series chipset. And this board is quiet high end which will perform nicely with good hardware. But it just fails to work. Want some help.