I think your DC jack is messed up, I had a friends laptop I worked on. He had the same problem at first, and one day it completely died. He brought it to me, I opened it up and replaced his (jack in )with a new one I bought online which cost $24 including shipping. If you know a friend or someone that can work on a laptop than ask them if they could replace your dc jack.
If you were in Denver, I could have helped you out.