Go into Control Panel >> Power Options and check the settings for "Choose when to turn off the display" which will be in the tasks list on the left.
If it's not that, check setting for "Change when the computer sleeps" (also in the task list on the left)
Thank you Phillip for your response.
Some Dell laptops commonly have issues with not waking from sleep properly, we have lived with that and tried every combination of settings to no avail on both machines. A BIOS upgrade did not help either.
The original issue was that the screen began to flicker then blacked out while she was using it. A reboot brought the screen back for about a minute then flickering to black again. There is no change if one moves or jiggles/jars the lid so does not appear to be the connection.
Occasionally after reboot it would work normally for an hour and once for an entire day then back to black.
That is when i connected the external monitor to be sure the graphics card was ok.
Soooooo, now the laptop screen works fine as long as the external monitor is connected. It dies to black when external is disconnected. I lean toward a bad switch on the backlight but do not know if it could be an over voltage issue corrected by the drain from two monitors?
It is operating fine but not portable