I just bought a set of nuts and went out to do my first trad climbing. later in the day i did a 22 called power finger, well 22 on trad is not so easy for a beginner and i happened to take a good 4m fall onto a size 10 BD nut. I then spent the rest of the day trying to smash it out the rock. I this piece still safe to climb on?

In a clinical environment the answer is almost certainly yes.
However what you have to consider is the damage done by the placement.
At the end of the day - this - like your decision to push the envelope on trad - is your call and yours alone.

Inspect the wire - it is probably a little bent - not a problem per se.
If any strands are broken they will in all likelihood be broken on the outside - due either to increased strain on the outside of the bend or from physical damage/abrasion. - If no strands are broken then I'd say that the chances are that the unit will still perform within specs.
The moment you suspect that any of the wire strands are broken I'd start to reconsider. -
Having said that : Rating on trad gear is all relative - and a significant portion of the time the rock quality or the method of placement will let you down before you exceed the gear's rating.
I've one or two broken strands in my rack - and I still climb on them - it's all a judgment call.

A caveat I often use particularly re ropes or harnesses is - when you're on that super-thin-might-well-fall-here-need-to-pull-it-out-the-bag scenario - will this cross your mind?
If so, then chuck it. Otherwise, go crank.

P.S - If you're talking about powder finger at monteseel - then kudos! It's a staunch lead even when your into the whole trad mindset.