Is it possible to reattach the v-brake spring/pin arm?
I'd start by unhooking the inner cable, like you're about to take the wheel out.

Then unscrew the big silver bolt that goes into the brake boss on the chainstay(rear) or fork(front)

Slide the brake arm off and inspect the spring.  If spring is in more than one piece, you'll need new ones.  Replace both springs to keep the tension close to even.

If everything looks okay, undo the good brake arm carefully and inspect how it goes together.  Reassemble the bad one repeatedly till you get it working right.  

Don't forget to use blue locktite/thread locker on the two big bolts.