With no more information that what you gave, it is like trying to play baseball in the moonlight on a cloudy night.
So, I am entitled to three wild guess, -Right?
strike one - The laptop battery is flat, you forgot the AC.
strike two - After changing Desktop Video, forgot a cable.
strike three - Bum install of Linux zapped the hard drive.
Hey, we are in the dark here. Some light please.
![Cool 8)](https://www.computerhope.com/forum/Smileys/classic/cool.gif)