I know this thread is dead, but I finally fixed it.
It was one problem after another, but here's what I fixed:
Safety was stuck
Sear spring was bent
Sear wasn't engaging
Pin that holds safety and hammer was out of place
And I touched up the scratches on it.
Works perfect, now.
Was this perhaps the result of someone trying to re-assemble the weapon incorrectly? They can be tricky and the manual goes into detail on how you have to do it to avoid damage.