It sounds like your TV is having trouble with the HDMI video signal from the Raspberry Pi, there are a couple things you can try:
- Use a different HDMI cable. While it's probably not the problem, it doesn't hurt to be sure.
- Edit the config.txt config file. Put the SD card in a computer (I'm assuming you're on Windows, but this'll also work on Mac OS X and Linux) and open it. You should see a file named "config.txt". Open it with Notepad and look for the line:
The "#" in front of the configuration option is a comment marker, it tells the Raspberry Pi to ignore that line of the config file. Remove it so the line looks like this:
This tells the Pi's video hardware to output a stronger HDMI signal, eject the card and see if that helps.
- Edit config.txt again, uncomment (remove the "#"'s) the lines:
This forces the Pi to use the lowest video resolution available.
If none of these work, try a different TV/monitor if possible.