When I install the video card on my HP notebook The screen goes Dark?

I Bought a used HP zv5466cl. When I install the nvidia driver from the Hp website and enable the device on device manager, The screen goes Dark and I have to restart with safe mode and Disable it again. Sometimes it will enable the video card and blank pixels appear on the screen. It becomes worse then not having a driver installed at all. now im stuck with default driver and the screen is blurry and pixeled. please help. p.s if this makes a difference, everytime I check the properties of my computer, the system GHZ changes from 798mb to 1.6GHZ but its really a 1.8GHZ|||Have you tried Windows Update?

Another thing is you might have to alter the display settings for the screen to display correctly at the correct resolution.

Its normal for the screen to go dark momentarily (around 30 seconds). It could be the powersaving feature also... does it do this with the power adapter plugged in?|||check the resolution of your monitor, what is the max. vlue your monitor can open, sometimes high resolution drivers used for low resolution monitors.