My DS lite will not turn on?

My DS is old, about 4 years.I never had any problems with it. I have drooped it a few times but it was fine after. I left it at a friends, I went to get another game. I can back to get it and I turned it on and the side lite came on and just went back off. but later that day it came on, but about 10 min in the game it turned off and it just did that for awhile. and today the lite just turns on.