Sounds like you need a new power jack.
This is very common with laptops, people yank on the cord and damage the jack, by jerking the connection loose or breaking the jack totally.
Try another ac adapter first to rule that out, then buy a jack on ebay and put it in yourself.
I used to fix laptops at work, they are very simple to fix, you just need some small screwdrivers, sometimes they are star hex screws inside.
Thats an example of the jacks you can buy.