I had powerproblem making the computer constantly flick between AC and Battery, even when battery was not connected.
After removing battery and checking with a second adapter that they were ok, i figured it was the powerjack, might been a loose pin or so.
First i took it to the local computer repair store, but they wanted to change out the whole motherboard instead of just the jack.
When i found this page, i ordered myself the correct DC jack on ebay, and got it a week later, went to another electronic store with the motherboard and the jack and asked if they would solder it for me. Cost me 25 bucks + 10 bucks for the jack. A good alternative to paying 250$ for a new motherboard.
Video of a g74sx Dissaembly:
http://www.youtube.com/watch?v=9reQvIxQvGQ