So after upgrading to Ubuntu 18.04 LTS, the keyboard is not responding properly. Although at the boot-up when I have to type my password for disk encryption, it works fine. But after login to Ubuntu, it doesn’t. For example, backspace doesn't respond to me pressing it. Sometimes it does but often it stops responding at all. Like that, the number on top of the keyboard also stop responding however at the bootup it works fine.
I just found out why that was happening. No it is not a keyboard hardware error but rather it is one of the features of Ubuntu 18.04 LTS that did this.
So, apparently inside "Universal Access", there is a feature called as "Bounce Keys". Out of curiosity a couple of days earlier. I enabled it and due to this, the keyboard wasn't responding as quickly as it usually did.
Now that i have disable the feature, keyboard is working fine.
I have similar problem with 18.04, after last update, ubuntu won't boot up. So I go to recovery mode and fix broken packages. Ubuntu now working but the keyboard is not responding. I tried add modify BOOT_IMAGE according to http://stevesubuntutweaks.blogspot.com/2013/10/laptop-keyboard-stopped-working-after.html and reboot still no effect. So I decided to turn off and remove the battery and power plug, wait for several seconds, place the battery power plug back and go to again to see if the default keyboard can work just in BIOS. It can work now. So I continue booting with linux and it is working again.