Well it could be a few things. To start try...
1. Uninstall the keyboard driver.
2. Reboot the laptop (yes, without reinstalling the driver).
3. When it restarts it should reinstall the driver.
If that has no effect it may not be software but hardware. If that is the case you would need to check to see if something inside has come loose, or gotten on the keyboard that could be causing it to not register. It may even need replacing.
NOTE: If the laptop is still under warranty do not attempt to open it up and work on it, or have anyone else do that, as it would void your warranty. Instead contact the manufacturer about a repair or replacement.