Sorry to say but your TV is going to stay like that unless you get a new screen installed. Check to see if Proscan has anything on their website that may help you in the way of a recall or extended warranty for your set. My Mitsubishi had the same exact problem that started right after the warranty ended and it just kept getting worse, started with 1 line then 2 then a patch on 1 side then the other. I checked their website and they were offering extended repair time for my set and they came out to my place and replaced the entire screen. that was about 8 years ago and my TV has never had a single problem since, i haven't even replaced the bulb yet after 13 years of daily use!
I have had monitors wit this same issue and it's impossible to repair, it's the contacts that run along the very top of the screen are losing contact with the ribbon that connects on the individual pixels and lights them up across the glass. You might be able to squeeze it with your hands and get it to temporarily work but most likely you'll just make it worse. I tried it on an old dell 27" monitor super wide screen (most of the lines were actually off the normal viewing area, i should have just left it alone because it ended up with a huge area that was all colored wrong. I only pushed on the tape right where the lines were and they went away but as soon as i let go they came back even more. those contacts become contaminated and they get tarnished and loose their contacts, there's thousands of them across the top edge. They separate and they get more air in the area and it keeps spreading like rust. look for a new TV soon, Get a name brand to avoid these types of problems, you do get what you pay for.
I know Mitsubishi is not a brand you would think of when it comes to TV's but I have had a fantastic picture and only the one problem that they covered with a free extended warranty so if this set ever does finally quit I'll only be looking at Mitsubishi TV's from now on.
Hint:Read reviews before you buy any TV's, all manufacturers make bad ones. Find out which models run through bulbs quickly and avoid them, bulbs ae expensive and some are hard to find. Avoid all the bells and whistles, get a good sized monitor that has a good display and has plenty of inputs and don't worry about the sound quality of the speakers, chances are they will never be used. Always turn down the brightness on any TV to keep the heat lower internally and it will also make you light bulbs last for many extra years and will help to keep things like the ribbons from separating as well as keeping the boards cooler so you're less likely to have a malfunction from heat build up and your home will stay cooler too!