Remove battery if possible , Unplug power cord, hold down power button for 30 seconds. If this does not work then you'll have to either reset the os to factory defaults or reinstall the os from install media..
The Lenovo IdeaPad features a hidden partition that contains recovery software, called Lenovo OneKey Recovery System, used to manage and troubleshoot your computer. Lenovo OneKey Recovery System enables you to scan the notebook for viruses, create a backup of your current configuration or restore the PC to a previous state. Unlike System Restore, which reverts Windows settings without affecting personal data, OneKey formats and reimages the entire hard drive to a previous state. If you intend to sell or give away the IdeaPad, or want to improve your computer's performance, you can do so using factory reset. The Lenovo will erase all of your existing data so the IdeaPad runs like new.
Back up your data first...
Turn off the computer and press the Novo button, located to the left of the power button on the front of the PC.
Select "Lenovo OneKey Recovery System" using the directional keys and then press "Enter" to boot into the recovery environment.
Click "OneKey Recovery," select "Restore From Initial Backup" and then click "Next."
Click "Start" and choose "Yes" at each prompt to reset the Lenovo IdeaPad to its factory default condition.