Repairing a laptop today. Second time I've seen this fault. The power input connector had a very poor solder connection onto the motherboard, and had been arcing at this point. Possibly poor plating, as there was no way I could get solder to stick (or flow over) the troublesome connection.

Ended up doing the same as the previous repair - removed the connector and fitted an alternative type. Reassemble, and tested. Sorted. Parts cost? Less than £1.00. Pretty good considering the owner was considering throwing the laptop out, and buying a new one!