All good technicians will know that in all Nintendo consoles: DS lite, DSi, DSi XL, 3DS the console will turn on but will not shown any image if :
* WiFi card is damaged, disconnected or removed.
* Top or Bottom screen are broken, in short circuit or having the flat cable broken.
* In 3DS all of above + disconnected or broken cameras.
Recommendation: DO NOT HIT THE CONSOLE TO TRY TO FIX IT. Open it and replace or place the broken/loose component in place.
JMMA - Montreal