Problem- When I launched King of Fighters 2002 it was on windowed mode. so I went to settings and changed it to Full screen. but now the screen just shows black and I can't see anything. Need help

A quick google suggests that it may be a problem with your video card and if it supports Shader 3.0.

What are your system's specs?

If the game ran well before and you just want to be able to play it in windowed mode again, here's what you should do:

1. Press Win + R to open the Run Dialog Box.
2. Enter %APPDATA% and press OK.
3. Go to the directory \SNK\kof2k2nd\
4. Now you can either delete the file OPTIONS, or you can edit it with Notepad and change the line:
<fullscreen>1</fullscreen> to <fullscreen>0</fullscreen>

I hope this helps.