If you have media keys that don't seem to work, it may be related to a Windows service. Try this:
Click on the Windows Start Button and navigate to the Control Panel. Start up Administrative Tools and click on Services. Scroll down to Human Interface Device Access and ensure the service has started up. If it is not, click on restart the service and change it to startup automatically by double clicking the service.
Fixed my problem, recently experienced this with K70RGB
K70 RGB Media Keys Not Working
in Gaming Peripherals & Audio Troubleshooting
Posted
Fixed my problem, recently experienced this with K70RGB