Assuming you are using a genuine Dell battery...

First, try a different charge. Usually that message implies a charger has gone bad. Maybe you have a friend or relative that uses the same charger to borrow to test....

If it is not the charger, it is likely a faulty AC Jack where the charger goes in.

God luck.

Read the top sticky post in the Laptop forum. To test the adapter, remove the battery and use the adapter alone. If that works, something is wrong with the battery. If you bought the battery from Dell (and you should always get replacement batteries from Dell) contact them.