Done what experts couldnt do :)
One day the computer just didn't boot so I kept trying and trying, but I didn't know why the !&&* my computer wasn't working, so I removed the HDD to check if it was because of the HDD but it wasn't. HDD was working perfect. So I took it to repair shop to see what's wrong. They told me that just to check and tell me what's wrong would cost me couple of hundred bucks! Then to fix it another couple. I was so !#^&@@, as new MacBook is 1200$ so I'm not gonna pay almost 600-700$ to fix my 9-years-old Mac. So I bought new one. But then one day I thought it could it be just small connection problem that caused this problem so I wanted to give it a try and ordered the HDD cable.
I was right, it was just this small cable! As I changed it, it just worked perfect.
When something like this happens, forget about the local shops, just go to Apple Store and talk to those Genius guys! they have so much experience and really trying to fix your problem. Instead of local shop is just trying to get as much as money possible. Then after tell you that sorry they did their best and it's not working.