Brightness function keys +/- cannot increase the brightness on display. Other function keys are working properly. The issue is highly related to a Windows update which upgraded the graphic video driver to version 10.18.10.3958 released 2014/09/30 or 10.18.10.4276 released on 2015/8/17. These versions are known to cause loss of brightness control. Restoring the previous driver should also restore brightness control.
As Z500 and Z400 are not Windows 10 supported hence you're not advised to upgrade to Windows 10. Should you insist to install Windows 10 and have this brightness issue, please check out this forum peer-to-peer discussion.
IdeaPad Z500, Z400
- Go to Device Manager (how to enter Device Manager)
- Select Display adapters and scroll down
- Right click on Intel(R) HD Graphics4000 and select Properties option
- Go to tab Drivers in the pop up window
- Push the Rollback Driver button (If Rollback Driver is greyed out which means no earlier version was installed)
- Wait until it is done. Your system should recover the brightness and the increase/decrease functions in the keyboard.
- If the previous step does not resolve the issue, please upgrade Intel Video Driver to the latest.
- Windows 7 Intel Video Driver: Download here
- Windows 8.1 Intel Video Driver: Download here
- Check to see if brightness controls have been restored using the brightness keys.
This also happens when installing TeamViewer as it adds its own monitor driver. To fix it, please take following actions.
- Navigate to Start -> Control Panel -> Hardware and Sound -> Device Manager.
- In the Device Manager window, look for “Monitors”, then right-click your monitor and select “Uninstall”. Be sure to also check the “Remove driver” option. Once removed, click the “Scan for hardware changes” icon. Doing so should bring the brightness settings back.
- For both NVIDIA and Intel drivers, after performing this solution, you can restore the brightness via Windows Mobility Center (Windows+X).