problems with my toshiba 36A50....=(?

I love this tv and think it is one of the best toshiba has made, but recently the picture was going to half screen, then after a while, just a thin line exactly in the middle of the screen. if I would bang the case of the tv directly on the bottom, it would go back to full screen for a while, then start the problem all over until I could not resolve the problem by banging the tv anymore. can anyone help me with an answer to what this problem might be, so I dont get ripped off when I try to take it to be repaired?... I would really appreciate it because like I said, its a great tv and would be a shame to either scrap it, or allow someone to rip me off.
thanks for you time