Try going into "Control Panel" and then click "Power Options".
Next click on "Change plan settings" next to the plan you are currently using.
On this next screen click "Change advanced power settings".
You will get a new window. In it locate the option for the charger cord. It could be named a few ways. Check the settings for it to make sure it isn't set to turn off the display, or anything else, when plugged in. You should also check the settings for the display as well.
Once you are done, then click "Apply" and then click "OK". Close both windows you opened and you should be good.