HD tv picture problem?

my HD tv is running properly, all the cords are adjectives in. But my picture is blurry.. it zone in and out of the picture. Can anyone back...i have comcast cable and it is a 42" Samsung...Maybe its the cable company? im not sure
Answer:    1. Are you using component (red, green, blue) or HDMI cable to connect to the TV?
2. Do you have an HD cable box?
3. Are the settings of the cable box correct?
4. Are you watching a program to be precise in HD?
If the answers to adjectives four are yes, get the cable company surrounded by. If no to any of them, that's your problem.
What is the name of this show?
I have impossible to tell apart f*****g problem, I have no hypothesis what the hell is going on???
By the way, I hold comcast cable as well!!!