Cooling Issues

• Your graphics card generates a great deal of heat even at default speeds. Overclocking a card often pushes the stock cooling unit past its limits, requiring you to install a third party cooler. This could take the form of a heat sink and fan or more expensive water cooling. Buying extra cooling components also reduces the cost savings overclocking provides.
  
  

Voided Warranty

• Overclocking will most likely void your video card's warranty and may even void your system warranty. You can overclock certain high-end gaming computers and video cards without voiding the warranty, but this is the exception rather than the norm.
  
  

System Instability

• Mild overclocking usually produces few negative effects, but if you overclock your video card too much, your computer will become less stable. Overheating and increased power load can crash your system, for example. Some applications and games might not work like they used to. Returning the card to its default configuration fixes these issues.
  
  

Damage

• Overclocking can damage your video card beyond repair, especially if you do not have adequate cooling. Consider whether you can afford to replace your video card before changing the clock speed.
  
  Overclock your graphics card in small increments and test it as you go to avoid sudden damage. Even if your card runs fine it will likely have a shorter life span. This is not an issue for many people considering how quickly hardware becomes obsolete, though.