Is the Problem Hardware or Software?
Before you attempt random fixes, try to narrow down your problem: is there something wrong with the keyboard hardware itself, or is a software glitch preventing Windows from recognizing keystrokes? Figuring this out can save you a lot of time later on.
Reboot your computer and try to enter the UEFI or BIOS—usually by pressing "Delete," "Esc," or some other key as your computer boots. (It will tell you which key to press along the bottom of the screen.) If you're unable to enter the BIOS and navigate it with your keyboard, there's a good chance you're dealing with a hardware problem. If you can enter the BIOS, and the problem key(s) work fine within that menu, your problem lies within Windows itself.
Exit the BIOS without saving your changes and continue to some of the fixes below. You may have to hook up a USB keyboard to troubleshoot.
Reboot Your PC
If you followed the above advice, you'll have already done this, but just in case: have you tried turning it off and on again? A reboot corrects a thousand ails, as my old IT manager used to say. If you can't use the trackpad or mouse to reboot the PC, just hold down the power button for about 10-15 seconds to turn the PC off, then turn it back on. If that doesn't fix the problem, try booting into Safe Mode and see if that works—it won't fix the problem permanently, but it will help you determine whether your keyboard is faulty or not.
Reinstall Your Keyboard Driver
Sometimes the driver managing your keyboard can run into problems, particularly if you install third-party software often and/or you turn your machine off all the time without using the Shut Down command.
Open the Start menu and type "Device Manager." Press Enter, and expand the "Keyboards" section. If any of the items in this section have a yellow exclamation point next to them, it can indicate a problem. Even if you don't see an exclamation point, though, I recommend right-clicking your keyboard in this menu and choosing "Uninstall Driver." Reboot your PC, and Windows should automatically grab the generic drivers for your keyboard, which may cause it to work again.
If that doesn't bring the keys back to life, or if the Keyboard icon isn't even visible in the Device Manager, head to the laptop manufacturer's support page and install the latest drivers for the keyboard. (If there's no keyboard driver, try reinstalling the chipset and/or USB drivers.) You can read more about downloading and updating drivers in this guide.
Adjust Your Keyboard Settings
Certain software settings can cause your keyboard to behave erratically, even if they were intended to be beneficial. For example, if your keyboard's "Repeat Delay" setting is too short, pressing a key might type two or more characters. Head to your keyboard's settings by opening the Start menu, typing "Control Panel," and searching for "Keyboard" in the upper-right corner of the Control Panel window.
If, on the other hand, you notice a delay between pressing a key and that character appearing on screen, you may want to adjust the Filter Keys setting. From the Start menu, search for "Ease of Access," enter that menu, and click on "Make the keyboard easier to use." If Filter Keys is turned on, uncheck that box and press OK to see if it helps. (Similarly, if your keyboard is behaving strangely, make sure Sticky Keys is also turned off in this menu.)
Change Your Keyboard Layout
If your keyboard keys work, but produce different letters than the keys indicate, it's possible your language or keyboard layout got changed accidentally (or someone in your office pulled a decades-old prank).
If you're still in your warranty period, try your laptop manufacturer's tech support line. If they determine you're using a defective keyboard, you should be able to get it replaced at a service depot without too much hassle. Before you send your laptop in or surrender it to a service tech, however, it's alwaysadvisable to back up your hard drive or remove it entirely and hold onto it. That way you'll still have your data, which is the most important part of your laptop.
Having a key on your keyboard stop working doesn't mean you have to chuck your laptop altogether. Our fixes above should address the majority of possible issues, but if you can't get it to work, use a USB keyboard for now and get your laptop looked at by a professional when you have time.
You can replace it on Sysnapse