Hello @melik39605,
That's an interesting problem you have there. I'm just taking a shot in the dark here, but this sounds kind of like something I was reading about yesterday. According to what I was reading, sometimes inside a computer, there is a cold solder joint. That means there isn't enough solder or it wasn't done correctly, so it doesn't make electrical contact. However, it was saying when the computer heats up, it can be just enough to melt the solder a little so it can make electrical contact. This could be your problem. The real problem would be fixing it. From what you said, it sounds like the problem resides in the display circuitry, so you would have two target that area. It might be worth shot to [guide|146683|pop open|new_window=true] the computer and poke around inside and see if you can see any obviously loose solder joints. If you do see something, I'll warn you that soldering can be very challenging, but not impossible. I fixed a computer that had faulty components on the motherboard and now it works just fine. I was a complete beginner and thought many times that I'd ruin the computer. It did take a lot of time and dedication, though. If you don't see anything, or if you don't want to deal with soldering, then I'd probably go ahead and [guide|145984|replace the motherboard|new_window=true]. Or, maybe I'm completely wrong and the problem is somewhere else. By the way, you didn't provide an exact model number for your computer, so all these guides are for one of the computers in the category. They may not be relevant to your computer, though. It would really help if you gave us your exact model number. If your exact computer isn't on iFixit, it would be greatly appreciated if you [guide|102668|created guides|new_window=true] for it so others can have easier access to repair info.
Good luck!