Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Why won't my Sonicare work?

I bought a sonicare set a few years ago. It worked but we didn't really like it, so we put it away in a closet. I decided recently to give it another try, but no matter how long I leave it plugged in, neither of the toothbrushes will work. What's going on? I can't see where one might install a new battery, so I am stumped.