Sony Vaio not charging

have a sony vaio vgn s150 laptop. when it is connected to the power cord it would try to charge the battery as well as go to AC Power.

My laptop is switching between ac power and battery intermittently. When I remove the power cord it goes on batteries but the battery starts draining quickly. Even when it is plugged in the battery would drain quickly and soon it would go on hibernate.

Please tell me how to troubleshoot. I have already replaced the power jack but it did not help. The power jack was not broken. How can I fix my laptop?

Please help. Thanks.