Why you need to know:
There are many reasons a computer keyboard may malfunction - from the introduction of a virus to the device to simple accidents. Instead of going out and spending unnecessary money on a technician or purchasing a new keyboard, try all troubleshooting procedures to find the source of the problem or rectify the keyboard functions.
What you will need:
Keyboard (that has malfunctioned)
USB or serial cables
How to get it done:
Let's say the keyboard is not working i.e. nothing is produced or occurs on screen after punching the keys. It may be that the computer automatically uninstalled the drivers (due to the presence of a virus that interferes with the hardware) OR automatically updated the driver which was incompatible with the operating system. Remove the keyboard (if it is an external hardware) and plug it, into another computer and see if this computer detects and/or installs the keyboard, allowing it to be used. Restart your computer and then reinsert the cable (after 10 minutes following start-up) into the port to re-establish computer-hardware communication; this should allow the computer to detect the new hard drive and install the drivers.
Another method is to open 'Device Manager' in the Control Panel or go to 'My Computer' and select Keyboard, right-click, (NB. Windows 8 gives the option to scan for recent hardware changes or conflicting software available in the options when user right-clicks on hardware type), 'Uninstall' or update drivers. Sometimes it is best to update drivers from the manufacturer's website. For example, if you are using a Sony laptop, on the Sony website it will give information on operating system, laptop model that are matched with the driver update. 'Uninstall', restart computer then select 'Reinstall'.
The steps above will help to solve the keyboard mistyping that is, you punch the letter 'K' and the letter 'Y' appears on screen. However, this may also mean one of two things. 1. The keyboard has dust particles interfering with the keys or 2. Numlock is on. For keyboards that need to be cleaned, try avoid blowing into the keys or using liquids and pointed objects to get in between the letters and numbers to avoid further damage and shortage. Compressed Air Dusters (canned air) are tricky, not recommended for laptop keyboards and best used on external keyboards when turned upside down. However, cheap battery-operated keyboard vacuums are available, starting J$200 and upwards. In terms of numbers appearing instead of letters, ensure that 'Numlock' is not on, especially if the keyboard is an older model or one with both numbers and letters on the same keys.
Helpful links: http://support.microsoft.com/kb/258826 or see simple troubleshooting tips for wireless keyboards http://www.youtube.com/watch?v=ON86CITHnB8.