Nintendo DS won't turn on. Green light flashes then turns off.

I am trying to fix a Nintendo DS Lite but not sure what the problem might be, and what to try to narrow down the issue.

When the power adapter is plugged in the orange light turns on so I don’t think the power adapter is the issue.

When I flick the power switch the green light comes on, then gets slightly brighter. Then the lower screen flickers (what I assume to be the backlight) and it switches back off (with the green light off and the orange one still on) This behaviour is the same without the orange light when not plugged in to the power adapter, so I assume it is holding at least some charge?

Any help would be much appreciated. Thanks