Pen Tip Not Working

I have only had my Bamboo Fun for a few weeks, and only used it twice. I recently went to use my tablet and it wouldn't recognize my pen tip or the buttons on the pen. The weird thing is that my eraser works just fine and so do all the buttons on the tablet. I hope someone has the answers! Thanks =) I have to finish my final project as soon as possible but after changed the pen tip, suddenly my pen didn't work... T-T