Hi,
Here are some troubleshooting steps that may help in identifying the issue.
- Start by uninstalling/reinstalling the keyboard driver.
- Go to Device Manager and uninstall the keyboard driver.
- Reboot the laptop once uninstalled, and it should reinstall the driver automatically.
- After the reboot, do test it again and see if the same problem will persist or not.
- Next to try is to check if the keyboard layout is set correctly.
- And lastly, do connect an external USB keyboard and see if it will work normally.
- If it does work normally, that means it's the keyboard that is faulty.
Here's a replacement keyboard for your laptop:
http

/www.amazon.com/Laptop-replacement-keyboard-Lenovo-Z70-80/dp/B00Y1VNU1K