Not detecting an adaptor

Hi-my Dell Inspiron 15 model 3558 gives me the message that it doesn't detect the adaptor that I am using. The battery is now dead because it won't charge. I went out and got a new adapter and cord, because I thought that might be the problem, but I still get the same message. How can it not detect the adapter that came with the computer? My warantee is up in three weeks, but I use the computer for work, so I don't want to send it in if I don't have to. Has anyone else had this problem? Thanks!