Here's a youngster on YouTube messing with a spacebar
http://www.youtube.com/watch?v=mKzNWd_WtW0
When my keys misbehave it's usually food debris - I take the key cap off (or the spacebar) and brush the rubbish away.
Good luck...
Alternatively - keyboards are cheap - Amazon £7.88 post free!
Peccavi, May 2013