I have a N4050 laptop that does not start . When inserting the DC power plug you get the following LED code

  W A A A A W A A A A W      W= long white A = short amber

The screen remains blank during this sequence and it does not repeat until the dc plug is removed and reinserted. 

Before this fault appeared the laptop had been working but slow and then just refused to start up.

The battery does not charge and appears to be dead, but it looks like the fault is more than a battery fault as it doesn't work on DC supply which is a Dell original and measures 19.5V. It is normally used on external power.

Any help would be appreciated.

Thanks