A Bluetooth mouse or keyboard fails to reconnect after being left idle

1. Your computer has a Bluetooth radio
2. The Windows option "Allow the computer to turn off this device to save power" is set.
3. The keyboard or mouse is Bluetooth 2.0, 2.1, 3.0, or 4.0.

 
You can check these settings by doing the following:

Windows 10:

1. Right-click on Start, and select Device Manager.
2. In Device Manager, click the arrow next to Bluetooth, and select the Bluetooth radio.
3. Right-click the Bluetooth radio and select Properties.
4. Select the Power Management tab, and see if there is a check next to Allow the computer to turn off this device to save power.
   
   

Windows 8:

1.  Select the Search charm and type Device Manager. 

2.  Select Settings.  Device Manager should be listed in the results.  Click on Device Manager.

3. In Device Manager, expand Bluetooth and select the Bluetooth radio.  

4.  Right-click on the Bluetooth radio and select Properties.

5.  On the Power Management tab, Allow the computer to turn off this device to save power is enabled if the checkbox is checked.


Windows 7:

1. Click the Start button and type Device Manager in the Search box. 

2. Click on Device Manager in the Results window.

3. In Device Manager, expand Bluetooth and select the Bluetooth radio. 

4. Right click on the Bluetooth radio and select Properties.

5. On the Power Management tab, Allow the computer to turn off this device to save power is enabled if the checkbox is checked.