It could be that the driver is incorrect (happens often), the keys are dirty (dust, debris, liquid, etc.), the keys could be damaged or the whole thing could need replacing.
NOTE: If you need to type in a password to even get into Windows to do the following, make sure you attached an external keyboard first, to get past the password. Then try the following... just make sure you disconnect the external keyboard while the system is reloading.
Uninstall the keyboard driver.
Reboot the computer (without reinstalling the driver).
When it restarts, it should reinstall the driver on its own.
If this doesn't work, you may wish to try connecting/reconnecting an external keyboard and see if it works fine. If it does, then it could be the keys themselves that are the issue.
Additionally, if your device uses one, you may want to try updating the Synaptics Driver if the above doesn't help.
You may also want to check the device for malware, viruses, etc., which can interfere with normal operation.