Go back an check to make sue that ALL the connections are proper. Free of dust, Locks in place, ribbon cables IN all the way, wi-fi board IN snug, ALL FOAM PADS back in place to prevent electrical shorting....also, THERE IS a FUSE inside the DS Lite. Google it, or search it here in AcidMods.
I took apart my DSL and put it back together. I had the SAME problem.
The light turns green.....gets a lil brighter..........then screen flashes and DS shuts off auto motto blotto gotto.
My PROBLEM was that one of the ribbon cables that connects the digitizer to the motherboard wasn't fully connected.
I tested the DS with everything connected WITHOUT putting it all back together....and Everything was running Fine.
.......THEN i put all that junk back where it post be.