Now I really need help.

None of my digital pins, except for pin 13, work. They all ouput ~4VDC and almost no current-- a 3mm green led plugged in to any of them stays off. (I wrote some simple code which pulls pins 2-13 high.)

did you remember the pinMode(n, OUTPUT); statement in setup? the behavior you describe is typical of leaving that out, in which case writing HIGH enables the internal pull-up resistor (about 30k[ch937]; very weak.)

Thanks!

And you have a 330ohm or so current limit resister in series with your LED also so you don't damage the output?

Yes.