Beeping sounds from my dell adapter?

I have bought this laptop(dell latitude D820) just a few months ago.. but the adapter seems dead . some strange beeping sounds come from it.. no green sound either.. also when it happened it shut down although the battery was full.. I took out and put back in the battery and it started working and it is running on battery now.. I could understand the adapter is dead, but why did it turn off although the battery was full.. and why did it start working just after removing the battery and puting it back in??