|What's your interpretation of "new"? When did you buy it ?|
Laptop main batteries usually work as they should for a year or so, then they begin to rapidly deteriorate. From what I've seen, by two years they cannot be charged to anywhere near their full capacity, and it gets worse after that.
They often develop internal shorts when they are older. If the battery gets HOT rather than just warm after you have attempted to charge it for at least a half hour, or after you have been using the laptop for a while with the AC adapter plugged in, it's definitely internally shorted and you must replace it. Internally shorted batteries getting too hot have been known to cause the laptop to catch on fire.
Some say modern laptop computers should work fine when connected to only the AC adapter - but I believe they often can't. Whether your model can or can't I don't know.
If it's still under warranty take it to a local laptop place that is authorized to work on Gateway laptops and have them analyze it.
If it is not still under warranty see the info I pointed to. You MAY be able to find a free or cheap service manual on the web for your model or model series.
If that doesn't help, then do the same as the above.
The data on the hard drive is probably okay, and you can connect it to another computer one way or another and copy whatever data you want to off of it.