Sorry to hear about your problem, I will be happy to help. I hope you find the time and information I provide to be valuable and will honor the good faith system of this site. Please be aware the answer to your question may not be good news and the procedures that are required to solve your problem may be complex and could involve replacing parts that can be expensive.
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There is probably nothing that is failing on your setup it's just the nature of digital connections to once in a while get errors. Every time the Tv has to change resolutions it has to go through the digital "handshake" process and once in a while an error will occur causing strange things to happen (like loss of audio). Some major manufacturers have software updates that can remedy this, but Polaroid is not one of them.
Your best bet is to set the cable box to always output the same HD resolution. This can be different for every cable service and box. For comcast- leave the Tv on and only power off the cable box, now press MENU on the comcast remote, in a few seconds a hidden menu should appear. If there is a setting for 4x3 override that is set to 480 something, then change that to stretch or something that will not make it switch to 480. To exit just press MENU again, then press power to turn the box back on, try some SD/HD channels to test your work.
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