It could be any number of things really, but either way you will need to open it and inspect the circuit board, (unless it's in warrently still in which case take it back) chances are it will have damaged more than one component aswell. It is quite common for the adaptor to break off the circuit board and usually it is quite an easy repair, but it sounds like it has shorted past the adaptor and taken something else too.
The HDD will probably be ok and you could slave it to another computer/laptop to recover all the data.