Keyboard certain keys not working

Hi, i have a 7577 and a while ago its z and x keys stopped working and then then would work after the laptop had been used for a while. So i handed it over to a tech shop and they couldnt fix it and when i got it back some other keys stopped working aswell and this time they didnt work again no matter how long i used it. 3 other new replacement keyboards were having an issue with the same keys however a usb keyboard works fine. Ive tried all other basic fixes but nothing. Also i gave it to the same tech shop again and they told me its a possible issue wtih the motherboard and its not worth the risk to mess around there, but for obvious reasons i distrust those guys. Can someone figure out this problem, would be a big help!