My son's ds lite doesn't start;

I would think that this is due to a poor connection to your top screen or like christian mentioned, a broken screen. Nintendo DS Lite Top Screen Replacement The issues are either that the connection is loose that holds the top screen ribbon cable to the board or that the ribbon cable to the top screen is damaged and will require replacing.Your DS power light will flash briefly but is is not going to boot because of these issues. http://www.buy.com/prod/top-screen-for-n... has the screen for sale, of course I am certain there are plenty of other places like ebay.com :-) Good Luck and let us know if it worked.