Check the power cord connection and power supply. 
  Is the cable connected correctly? 
(Connected using the D-sub cable) 
Check the DB-15 cable connection.    
(Connected using the DVI cable) 
Check the DVI cable connection.  
(Connected using the HDMI cable) 
Check the HDMI cable connection. 
(Connected using the DP cable) 
Check the DP cable connection. 
* DVI/HDMI/DP input is not available on every model. 
  If the power is on, reboot the computer to see the initial screen (the login 
screen), which can be seen. 
If the initial screen (the login screen) appears, boot the computer in the 
applicable mode (the safe mode for Windows 7/8/10) and then change 
the frequency of the video card. 
(Refer to the Setting the Optimal Resolution) 
If the initial screen (the login screen) does not appear, contact the 
Service Center or your dealer. 
  Can you see "Input Not Supported" on the screen? 
You can see this message when the signal from the video card exceeds 
the maximum resolution and frequency that the monitor can handle 
properly. 
Adjust the maximum resolution and frequency that the monitor can 
handle properly. 
  Make sure the AOC Monitor Drivers are installed.