Battery is stopping charging after 68%

Hello guys,

I have a Dell Inspiron 15 3521 laptop.

I've have got some problems with my charger lately. When i'm plugging it in, it says: The type of adapter cannot be determined. Your computer  will work more slowly and the battery won't charge.

Normally when i try to plug it in, it works after a few times. However, Two weeks ago it stopped charging after 68%. 

It is a charger of Dell and I got it at November 2013. 

Thanks in advance!