If your keyboard stops working after your system has been inactive or wakes up from sleep, try modifying your Bluetooth adapter's power settings.

1. Launch Control Panel > System and Security > System > Device Manager.

2. Under Bluetooth Radios, right-click on your Bluetooth adapter (ex. Dell Wireless 370 adapter), and then click Properties.

   

3. In the Properties window, select the "Power Management" tab, and clear the check box "Allow the computer to turn off this device to save power".

   

4. Click OK and then reboot the PC.

If this solution doesn't work, restart your computer. See answer 360023413233 for additional information on connecting your K810 keyboard to a Bluetooth device.