Follow the step-by-step method and see if it works.
# First, while the computer is off, connect an external monitor.
# Next turn on the computer and allow it to fully load.
# Once loaded, press the "Windows Key" + "P" to open the "Easy Display Switcher".
# In here select "Computer only".
# Now shut down the computer and disconnect the external monitor.
# Disconnect the external monitor
# And finally restart the computer.