Default [Q] Screen problems - crazy behavior, not responding

Hi,
I have red all the topics with the "screen problem" and I think, I'm very close to this described problem (hardware problem)
http://forum.xda-developers.com/show...screen+problem
but I would like to ask you once more. I bought the phone used, the seller told, that are only software problems after flashing to 4.3.
I tried hard reset, restore the stock rom via Skipsoft Android Toolkit, restore the stock rom 4.2.2. and 4.3 via Odin, nothing helped.
The strange screen behavior begins a few minutes after booting to system.


The problems are shown on the video
http://www.youtube.com/watch?v=vzMg0RQxF_g

Please, have someone any advice? Or is it really a hardware problem?
The seller wont take the phone back