First I'd verify that its the TV, and not whatever is hooked up to it (VCR, DVD, cable box) that is causing the intermittent picture.
As cheap as new TVs are, and as expensive as repairs are now, unless your TV is high-dollar (say $700+) or has some personal value to you (such as TVs built into wood cabinets that you can't get anymore), I'd say trash it and go get a new one.