Answer to: Trouble with shoulder buttonsNintendo suggests using a dry, clean toothbrush to 'scrub' the dust out. I find that this works intermittently. As Mr. Eisenman pointed out, if you aren't gonna open it, there's not much you can do. Email me at firstname.lastname@example.org for any further questions/info.
Answer to: My DS fell and doesn't turn onUnfortunately, Nintendo has a fail-safe in their DS systems to discourage hackers. If any screen is disconnected at all, then the DS won't boot up. When you turn it on, does your green light come on at all? This is very important as to what the cause is, but it's most likely just a semi-disconnected screen cable.