A user reports that they walked away from their laptop for 30 minutes and when they came backthe screen was very dim. The user tried moving the mouse and increasing the brightness setting,but neither worked. Which of the following should the technician do FIRST?（）

A. Plug in an external monitor to test the video card.
B. Run a check disk scan to verify there is no corruption.
C. Check if the laptop is now on battery power.
D. Have the LCD screen replaced with a known good screen.