Dell lattitude Screen

I do not know enough about pc. I have a dell E6420 laptop. My neice was trying to load adobe reader. She came and told me the screen was flickering and the color was blue and pink art work. I restarted it and remove from the download folder adobe.

The screen is now pink, until you enter the password, then it becomes blue and pink swirl artwork.

I perform SFC scannow, CHKDSK on the command line, and perform tests by pressing F12; in all cases no defect was found. I also perform diagnostic test in safe mood.

i think she may have dropped and did not tell me.[note]

I plugged an external monitor and the display is okay. Question: do I have a driver problem or defective screen, board or cable. Thank you for any help.