I have a 42 inch flat TV with ambilight, it's about 5 years old. The picture will randomly go very dim where you can barely see anything. When this happens it typically comes back in about 10 minutes. Comcast has already installed a booster. Not sure if this is related to the cable or the TV itself. I also do not have HDMI hooked up, as I don't have an HDMI box yet.

Also, another issue I'm having is when it is cold, my TV will not stay on until I turn it on about 15 times. It will turn itself off immediately until it gets warmed up.

Your backlight could be going out on the TV. To test if it is the cable or not, try connecting something else to it and switching to that input. If it happens on all inputs, I would invest in a new TV. To fix the one you have will actually exceed the value of the TV and even the cost of getting a new basic 42" HDTV.