Greens instead of blacks. Temporary fixable, but not permanently

Hello,

My mum has unibody macbook pro 2009 17" (3.06)

It has an annoying problem - it displays greens instead black, and it can be fixed temporarily by pushing the middle of palmrest over the keyboard (there is a radiator)

I suppose that it is caused by faulty flex cable. Did anyone have similar problem?

Thanks for help in advance

I replaced thermal grease. And happened something after reasembling the computer. I noticed that screen goes green when i push the bottom of the laptop around place shown on the photo