The Lenovo G580 screen will turn off when I plug in the charger. It will still charges the battery but I cannot use it when it is plugged in. The battery lasts several hours so I believe it is good. I checked the sleep mode settings in the power options and they seem OK.
When you checked the sleep mode settings in the "Power Options" did you go all the way into the list of all settings and check the "Display" settings and also the "Plugged In/Charging" settings?
If not, go into "Control Panel", then "Power Options". Click on "Change plan settings" next to the plan you are using and then click "Change advanced power settings." In here locate the options for being plugged in/charging and also for the display and make sure neither is set to sleep or hibernate. You may also want to just check all settings listed to make sure it isn't something else.
When I went through the "Power Options" I changed or verified all the settings that deal with turning off the display, The display still turns off when the charge is plugged in and comes back on when the charges is unplugged.