Toshiba Television Issue

Hello everyone.  I happened across your site here when I was looking online for some help with an issue that I am having with my television and I hope someone here can help me.  It is a 32" Toshiba (not HD or Flat screen even) and I purchased it from my work at a very discounted price, so I do not know a lot of history about the television, but I can describe the problem I am having.  Sometimes when I turn on the TV, it works fine.  Other times, a line will appear at the bottom of the TV and work its way up to about the bottom 1/3 of the TV, and at that point, the picture shrinks down and is somewhat distorted.  The picture is still showing across the TV from side to side, but from top to bottom it shrinks.  At first, I could just hit the TV on the top (not too hard) and it would fix it for a day or two. Now, that doesn't work, and I do not want to damage the TV by knocking the heck out of it.  Does anyone know how to fix this problem without having to take it to the shop?  To me, it would seem that something is loose on the inside, and would just need to be reconnected better, or even perhaps soldered.  Any ideas?  Thanks!

WhizKid

Update:  Now the screen went blank.  The picture will sometimes show up , but only about 1/4" tall, and stretching all of the way across the screen.  I took tha back off of the TV and looked inside.  I am pretty sure that smacking the TV made whatever was loose worse (oops).  I suppose I know now the error of my ways.  There are two small knobs inside the TV labeled SCREEN and FOCUS.  I can make the screen go blank by turning one, or make it come back on by turning it the other way.  And no, I am not stupid enough to do this with the power on.  haha