Screen displays little squares instead of picture, when you first turn it on there is a picture for a split second, then it goes back to digital squares.Everything else works fine, sound, channel functions, guide for the cable is visible on the screen, but channels are all digital squares.

SOURCE: can't get all cable channels

Chech with you cable company to see if they switched to the higher chanels. I do not know if you are connected directly to the antenna or a cable box.

SOURCE: 37" Polaroid LCD TV No signal appears when select channel

I was having same problem, and think I got lucky and found fix.

Try unplugging the TV and waiting 30 seconds, then plug back in.

You will likely get blue screen with "No Signal".

Go to Menu, then scroll down to "Setup". Select "Factory Reset" then hit "Yes."

This did it for me. Wish you all luck.

SOURCE: black out

Try turning off the Closed Caption..

SOURCE: change channel, lose picture. power off/on, picture appears

switched HDMI plug from HDMI1 to HDMI2 port and that solved the problem

SOURCE: Can't fix polaroid tv help!

Well a couple of questions if I may.
1) How do you have the TV connected to the Cable box?
A) Composite cable 'usually a yellow colored RCA to another Yellow RCA connector' and then plugged into your TV's Video input. This will only give you 3x4 video aspect as its only limited to 480 lines of resolution. This would explain why you only get a 3x4 aspect.
B) Component cables, Usually three cables 'RCA connector's 'Red, Green and Blue' colored ends.
This will give you output resolutions of 720i up to 1080P which is your High Definition outputs and will fill your screen from top to bottom and side to side if your cable box can actually receive High Def. It should since all local Television stations had to go to Digital HD last June 09.
Happy Thanks Giving,
Blessings always,
A/V Media Tech Guy