Won't power on - at all. What to do/replace?

School computer for student use was brought to me with complaint: running on battery-only, unexpectedly powered down. I charged with known-good outlet and power adapter for over 24 hrs. At first the magsafe light would alternate green-orange, later only a VERY dim green glow. Pressing the power button has no noticeable effect - no noise or light. I've reset the SMC numerous times; swapped the RAM around; tried with and without battery.

Condition: magsafe port is clean; some damage to the case - probably voiding Applecare - topcase is raised somewhat near IR receiver, bottom case has hairline crack near join of topcase to left of trackpad (damage appears old); power button is SLIGHTLY depressed (but has satisfying click feel when pressed).

From reading here, I'm guessing it may be the mag safe board or topcase - but I don't know which is more likely, or maybe something else.

Suggestions?

BTW, this site is awesome!