nhan le try this one first:

Check the battery pack and ensure its charged [LED light on upper right corner should be lit GREEN].

-If AC wall power adapter is being used, ensure both the connector [into DS lite] and wall plug [to outlet] are securely connected.

-Check the battery contacts and clean if necessary using a pencil eraser or lightly scrape contacts until entire surface is shiny.

-Check the placement and orientation of battery pack to ensure its connected securely and properly.

Read more: How to Troubleshoot Nintendo DS lite Issues | eHow.com http://www.ehow.com/how_4584340_troubles...

If that does not work, you may have to disassemble your DS lite and check on the cables, connectors and logic board to make sure all connections are seated properly. Good Luck