If you feel it is a hardware problem then you could need a new video card. But before you shell out the money for a new card you might want to eliminate some of the other causes first. The more common ones are problems with the drivers
as I mentioned, but barring that the hardware issues are usually Memory (errors and defects), Unstable Overclocking or Incorrect motherboard voltages, Poor Cooling, Power Supply,and Video Card.
It helps if you can isolate the actions that trigger the event. Most often it will be an application using 3D graphics. But if the incidents occur constantly it would point more towards defective hardware. If it happens more specifically (just when running Game X) it points towards overheating, settings, software, or driver
issues. GENERAL SYSTEM PERFORMANCE
You need to eliminate the possibility that your computer has a global problem. You can use a program like Prime95
to stress test your system. Free Software - GIMPS
You can run the "Stress Test" for a few hours or overnight. This will not tell you what the problem is, but it is helpful to uncover any issues your system has with instability and cooling. OVERHEATING
You can check your temps by looking at your BIOS readings or use a free program like Speedfan SpeedFan - Access temperature sensor in your computer
A real easy test is to just pull the side panel(s) off your case (You can also blow a house fan directly into the open case) and see if the problem goes away or gets better. If it does then the issue is definitely overheating. If you are overheating you need to look at installing some cooling upgrades. You want to look at ventilating the case (more or bigger fans), Upgrade your case to a larger gaming case (lots of fans, water-cooling), etc. MEMORY
Memory errors can cause video problems. Run a program like Memtest86+ for at least 3 passes to see if there are any memory errors. Memtest86+ - Advanced Memory Diagnostic Tool
Go into the BIOS and check your motherboard voltages against spec. You could also reset the BIOS defaults if you think any alterations or overclocks you have made may cause system instability.
Check that your power supply has sufficient wattage for your system. Keep in mind that a power supply loses power as it ages.
If you can borrow a known working video card to test in your system that will tell you if the on-board graphics are no good.
Hope that helps