I Just Got a New Hdtv and When Playing Halo: Reach on the Xbox, the Sensitivity Has Gone Weird.?

Got a new 37" Samsung LCD HDTV and I tried out the Xbox 360 on it, playing Halo: Reach. But, the sensitivity of the gun shooter thing went weird, like it was heavy. How can I fix this?

Suggestion:

press the start button and go to controller setting and it should be there