It appears to be in a deep sleep not responsive to mouse or keyboard.  Need to go inside power management to disable deep sleep. there are other possibilities read this “Steps for Fixing Windows Computers that Do Not Wake Up or Resume from Suspend or Hibernate Mode but Will Power On”  
I have an Inspiron 3455 , after using the computer I'll come back to use it say after 2 hours, I get a black screen. This is the second time it's happened. I turned it off and on a few times but nothing happens. The only way that i can get it to come back on is by unplugging the power cord on the back of the computer.
black screen