Nvidia drivers causing lag on Windows 8.1

**Note: (English is not my main language so I'll do my best to explain my problem correctly)

First of all, [here](http://pastebin.com/CJVE0hCy) are my system specs.

Okay, so now I am going to try to explain what happens whenever I boot my PC.
All goes well until the Windows login screen is shown. I press enter to get to my user and the custom picture goes upwards, lagging. I put my password to enter to Windows and the loading thingy shows up, also lagging.

When the desktop is shown, I can start moving my mouse, but it lags a lot. Sometimes I get reports such as "Display dirver has stopped responding and has recovered". Below that there appears a text saying this: "Display driver NVIDIA Windows Kernel Mode Driver, Version 344.75 stopped responding and has successfully recovered".
I have to mention that there is lag not only on my mouse movements, but in Windows generally. For example, I use Windows+C to open the sidebar and it also shows up lagging.

I have also got Blue Screens of Death, but just a few times. It says [DPC WATCHDOG VIOLATION](http://gyazo.com/3cfea51a5f3db648ff1fcd72f8fe81d3)

To fix this lag, I need to restart my PC.
When I restart, there is no lag in the login screen, neither in Windows.

I uninstalled my GPU drivers and started using the Windows basic one, just to see if the lag dissappeared by not using NVIDIA Drivers.
So, I started in Safemode, and used DDU to uninstall my drivers. Then I switched my PC off. After that, I started in normal mode, while using Windows basic driver, and boom! There was no lag.

I decided to install NVIDIA drivers again, and while the installation was in progress, the lag appeared. Exact same lag that I described before.

I have reinstalled Windows, formatted... I really don't know what to do. Could it be because of a malfunctioning GPU?
The rare thing is that once I restart, the lag disappears completely and I am able to get (at least) +90 FPS in games like CoD: Advanced Warfare and such.

I really don't know what is happening. The one thing I'm quite sure of is that NVIDIA Drivers make my PC/Windows lag and even crash sometimes.

Can anybody help me? :(