As it says, I've got a couple 68k Powerbooks (a 170 and a 180) which don't want to power on. The 180 I know worked when I got it, but evidently it reached its shelf life and now it doesn't; the 170 I'm not sure of, as I just got it from the recycle center, but it's otherwise in good shape. The AC adapter is known-good, so I don't think it's a problem with that; what else should I check in trying to restore these to life?