I've known a few people who've had similar/exactly the same problem. actually, i just did repairs on 2 Identical
Gateway mx6447 models which are known to have that same issue. I thought it was funny because the customer has twin daughters and they not only had the exact same laptops, they also had the same problem at the same exact time!
there are a couple of things you may want to know about this:
1)when a DC Jack fails, it generally does so over time, like you said...there was a warning sign before it went, usually it works only in certain positions. this would normally be "good enough" but this constant "on/off" status causes voltage spikes and drops, possibly even "arcing" which might damage not only the motherboard but also additional components.
2)if you attempt a repair with the improper equipment ie: if you only have a store bought soldering iron, it may not be enough to complete the repair...besides the actual joints visible, there are "sandwich" joints in the motherboard itself, without appropriate care these joints will be damaged and there will not be a solid connection. these repairs arent recommended to be attempted if you are unsure. in many cases it may result in motherboard replacement...besides the added difficulty of disassembly which if your not experianced in, may result in damage to other components of course.
...ok so what now?
well there are a few different ways to fix this problem.
feel free to e-mail me or vice versa for more detailed information as to where to find a fix!: