ten to one you're problem is simple and caused by corrosion or a lack of lubrication.
As long as the corrosion isn't severe both are cured the same way, with a few drops of light oil. Start by adding a drop to the lever pivot and the brake pivots, and work it in by working the brake lever and if necessary pulling the brake arms open, for a few cycles.
Then use a bit of string to hold the calipers closed, which should give you some slack in the cable. If the brake has a tension relief mechanism open it for more slack. This should give you enough room to pull one of the housing away exposing the inner wire. Drop oil on the wire and let it wick into the housing. Sliding the housing back and forth within the available slack will help carry the oil down it's length, and add oil slowly until you feel the housing sliding smoothly.
Release the brake, being careful to guide the ends of the housing back into the ferules at each end and you should be good to go. If not a trip to the LBS may be warranted for a more detailed review and probably a cable replacement.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.