Why won't my Lenovo netbook charge?

Just now, my Lenovo netbook (S100c) Just stopped charging. I tried to check my charger but it was connected and then I tried to turn off my netbook and then charged it then it work!
When I turned it on, it was still charging but then the charging sign disappeared.
So I removed it and then few minutes later I placed it back in, the charging sign was on but after that it's gone.