Please answer these questions in order to understand the issue better.
a) What is the make and model of the computer?
b) Are you using wired or wireless keyboard?
c) Have you enabled the Num lock on the keyboard? Do you see Num Lock LED light turned ON, on the keyboard?
You may face this issue if the Num Lock on the keyboard is disabled or It is possible that you have switched the keyboard layout by accident.
I would suggest you to open the onscreen keyboard and check if these keys work. If these work in the onscreen keyboard, then the issue might be caused due to driver or a faulty hardware.
You can refer to this article to open the on screen keyboard:
If these work in the onscreen keyboard, then the issue might be caused due to driver or a faulty hardware. In this case, I would suggest you to try the following steps and check if it helps.
Method 1: Try Hardware and devices troubleshooter
The hardware and devices troubleshooter can detect and fix errors and incorrect settings in devices. You can run the built in troubleshooter in Windows 8 and check by following these steps:
a) Press Windows Key + X, select control panel
b) Change the ‘view by’ option on the top right to ‘Larger icons’
c) Select the Troubleshooting option and click ‘view all’ on the left panel
d) Run the ‘Hardware and devices ‘troubleshooter.
Un-install and re-install keyboard drivers from the manufacturer’s website and see if that helps:
Step 1: un-install the drivers:
Follow these steps:
a. Press “Windows Key + W” from the keyboard.
b. Type “device Manager” without quotes in the search box and hit enter.
c. Right click on the keyboard drivers and select “Uninstall”.
d. Restart the computer once it is uninstalled.
Note: Before uninstalling the driver, please make sure that you have downloaded the latest driver for the keyboard device from the manufacturer website.
Method 3: Your keyboard layout might be set for a different language than the one you want to use.
How to change your keyboard layout
Note: This article if for Windows 7 but holds good for Windows 8/8.1.
Also refer this article: http://windows.microsoft.com/en-us/windows-8/add-language-keyboard
Hope this helps. If you need further assistance with Windows, let us know and will be glad to help.