What it might be is that the computer is set to a resolution that your TV can not read. Try changing it until your TV turns on.
If no hope the only thing else I can think of is to update the driver for the graphics card. You can do this by using Device Manager.

For windows:
1. Go to start menu
2. Right click "Computer" or "My Computer" and select "Properties"
3.
XP - Click the "Hardware" tab and select "Device Manager"
Vista and 7 - Click "Device Manager" on the left hand side
4. Look for "VGA" might be under "Display"
5. Right click and select Update driver.

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