XPS 15 L502X display won't come back from sleep/hibernation

Follow the below mentioned steps to resolve the problem:

Click on Start and in the search box type "Device Manager" (without the quotes) - and hit Enter. This will open up the Device Manager. Double click on 'Universal Serial Bus controllers.' Now you will see a list of 'USB Root Hub.' Right-click the top one of these and select 'Properties.' Click on the Power Management tab, uncheck where it says 'Allow the computer to turn off this device to save power' and click 'OK.' Now repeat this action on the other 'USB Root Hub' items in the list.

When all the above steps are done you can close the Device Manager, and your USB mouse and keyboard will now be able to re-awake your computer.

If the above step doesn't work then follow the below mentioned steps:
Check if allow this device to wake the computer is checked in Device Manager.
1.    Click Start, type Device manager in the Start search box and hit Enter.
2.    Select keyboard, it will display your keyboard, right click and select 'Properties'.
3.    Select the 'Power management' tab.
4.    Check the "Allow this device to wake the computer" check box.
5.    Repeat these steps for Mouse and Network adapters as well.

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