Basically, I try to turn my DS Lite on and it doesn't do a thing.
The charger light goes on, however.
I don't know if YT is accepted here, sorry.
I can't say for sure, as I don't own a DS Lite, but the first thing that comes to my mind is that the power switch may be damaged or broken. Has the system been exposed to any hard or sudden impacts before?
The same thing happened to my DS Lite, which was used for about three years. The issue might be two things. Firstly, the power switch itself could have disconnected with whatever it is in the DS itself that turns the power on. Secondly, the DS could be experiencing some sort of electronic error. This is more likely (and what eventually was wrong with mine), but the only way to permanently fix it is to repair it. You can schedule a repair at 1800-255-3700 (6am-7pm, Pacific Time, 7 days a week).
I should note that whatever electronic glitch or bug causes this may eventually go away. I attempted to turn on my DS Lite 5 months after it broke and it worked all of a sudden. In any case, it would cost about the same or even more to repair your DS Lite (if the 1-year warranty is up) than to buy a new one. It is a better investment to get the DSi or 3DS.