Check to see if the tip of your AC adapter has broken off. They sometimes break off in the DC in port. If so and you can't get it out (very difficult) you'll have to do the replacement rab777 directed you to. I've had three customers who bought new AC adapters and then plugged them in with the broken tips still inside. That usually destroys the DC in port.
I have the same problem, the power cord just quit and the light at the computer end stopped working. I checked the tip and it is good, I also tested it with a volt meter and I am not getting power (DC) out. Is there a way to take the end apart that plugs into the wall and check the bridge rectifie and transformer.
Actually by follow the instructions for getting to the DC-in connection.
If you remove the rf shield
- at the back of the connector
- gently pull back on the top of the center tab
- form a gap that the tip will fit through
- you can push the broken power cord tip out the back of the connector.
Reassemble - get a new power supply - and away you go!
See my addition at the end of the DC-in repair guide.
(sorry for the bad picture)