Thank you for the reply!!
I have just plugged the USB keyboard and those keys on the keyboard works, thus, I assume the motherboard is intact and it is the issue of the keyboard itself. Am i right?
I ordered the keyboard from the eBay, however it is not shipped yet. Therefore, could you please tell me is there any way I can manipulate those keys from the inside? Maybe the keyboard connector unplug/plug can help? I opened the computer but as that connected is under the motherboard, I didn't disassmble it.