compaq presario r3000 power problems

I have had this notebook for years and it has been a great pc until lately. It seems that whenever I do anything on this computer it switches from ac to battery power. It does this so quickly and so often that it has ruined the battery that I purchased last month. The brand new battery drains in about 45 minutes and then immediately hibernates. . I have my settings set to warn me when the battery is @ 25% and to hibernate at 10% but by the time I get the warning it's too late. It doesn't even give me enough time to close the program that I am running. I have talked to compaq and have read some of the other postings.

Apparently there have been some problems with the AC jack, but I don't think thats the problem. If it was, then it wouldn't charge at all. Right???

Although I have copied most of the important information to my desktop, I don't have the $$$ to purchase a new notebook, and I need a notebook for some of my college courses.

Please Help ! ! !