Graphics issue on computer, please help

Post your build.

Is your CPU getting hot?

Maybe its a power supply fault. Find out the make and model.

In the first case you should check the temps of your graphics card with a temp monitor to see if there is anything abnormal.
If the temps of the Gpu on the card seem high even when at windows desktop then it can indicate anything from a loose cooling solution on the card it`s self.
Verify that the fan, or fans of the card are spinning and do not have any faults or may be damaged.

Next check the temps of your Cpu also. if high it will cause two things the desktop and screen refresh or update of the screen image can become sluggish and slow due to your cpu down clocking in speed to cope with a high level of heat build up of the cpu. You should check that the cooling solution for the cpu is fitted correctly and has not become loose or is ill fitted.

Intel stock coolers with push pin design are well known for the clips to lift on a corner causing improper contact with the cpu heat spreading plate of the cpu.

If all seems fine.

Then your next step is to determine if the video driver for the card you have is at fault.
If you had a prior graphics card in the system before the card that is currently installed.
You should of removed any of the old video drivers first.

As a test use driver sweeper below to remove any old entry in windows relating to a prior graphics card, and also remove any reference of the driver used for your new card. let it clean your system of video drivers, then restart your system.

http://www.guru3d.com/content-page/guru3d-driver-sweeper.html

Now go and get the latest driver for your graphics card from the Nvidia website driver and support section and install it.
See if stabilizes the screen problem.

Another thing to watch out for is Adobe flash player or shock wave. A bad installation will cause screen tearing and screen glitches. Java can also cause problems check that it is installed or up to date on your system.

Then were down to the crunch, if none of it resolves the problem, then the slowdown and black out`s ect will be related to your power supply if over 5 years old degrading. not providing a constant smooth flow of electricity to keep the graphics card stable.
The same will also apply to your cpu as any dip in voltage would cause the core speed of your cpu to drop causing a glitch or slowdown of windows desktop and screen update or refresh of icons ect.

Such things as power regulation of a Psu can cause havoc with graphics cards and are sensitive to voltage changes, or small periods of low voltage supply from the psu it`s self.