High end PC Lag while Gaming

Hi,
the following are the specs of my computer:
Asus P8Z77-V- LX2 Motherboard
Intel i7-2600CPU @ 3.4GHz
16GB RAM DDR3 668.5MHz
NVIDIA GeForce GTX 780 Ti

I lag on almost every single game, including League of Legends, Maple Story, DotA 2. Most of these does not lag on my low-mid end laptop and I find it very annoying why has it been lagging on my PC. I thought it was a faulty graphics card back then when I had the ATI 6970M graphics card then I upgraded to the GTX 780Ti and it still lags.

I notice miracle happens when I was using my 6970M graphics card, whenever I uninstall and re install the driver of the graphics card at the "Manage my computer" program, the lag disables and I am able to play all games with no lag. However, after restarting, the lag resumes and I must repeat the same step to remove the lag. However, with my GTX 780Ti, it does not work.
 
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