DS Lite wont turn on.

I have an idea it might me that the top screen or the bottom isn't plugged into the circuit properly.
The top circle is the bottom screen plug and the bottom circle is the top screen plug. Make sure that the end parts of the wires (black, browny part) are slotted in fully (not the black, browny bit sticking out to the side so don't try to force those bits in or else you will damage it).

I didn't fully slot in the the top screen plug and my ds turned on then after a second or two it turned off. Hope this helps you. ;D

 

Maybe the voltages that went into your ds weren't correct.

The DS uses an ac adapter.

 

my top screen broke of too didn;t work like that just call nintendo that the screen is broken and listen what they tell you maybe you can send it back too them if they say so

 

But if you opened it and modified it, they won't take it.