Please do try these troubleshooting steps that may help.
- Start by uninstalling/reinstalling the keyboard driver.
- Go to Device Manager and uninstall the keyboard driver then reboot the laptop.
- After the reboot do test the keyboard again and see if the same problem will persist or not.
- If it will still not work, do try an external USB keyboard and see if it will work normally or not.
- If the external keyboard will work properly, you'll need to reinstall Windows itself to correct the problem.
- Here's how: http/www.dell.com/support/article/us/en/19/DSN_362066/en
- And if all these will not work the last option would be to replace the keyboard itself.