There could be a number of possible problems for this:

• The connection is to the laptop or TV could be bad
• The cable itself could be dodgy
• Your have a low-end graphics card that can't support the TV input requirements
• You are using some sort of converter which is interfering with the signal quality.
• Your laptop's output configuration is not configured properly - check the resolution and screen refresh rate and ensure you laptop output and TV input support it
  • To adjust the output, presuming Windows 7, right click on empty space on your desktop, select "Screen Resolution"
  • Click "Identify" to ensure you are modifying the correct screen
  • Ensure the correct display is selected, and adjust the resolution to one that is compatible with your external display.
  • To adjust the screen refresh rate, click on "Advance Settings", select the monitor tab, and adjust the screen refresh rate to one that is compatible with your display.