Battery works but wont charge battery wont run off ac power supply but ac power supply is good will run my other laptop

Hello, you don't mention the model number, but there was an issue with the power connector mounted on the mother board of certain Dell laptops causing the type of problem you've got. Dell refused to address the issue until a group of users in the USA threatened a class action against the company, then Dell agreed to repair all affected laptops and extend the warranties. It's possible that yours is the same problem. Unfortunately, if you're NOT in the USA you wont get it remedied for free. As you don't state the model, I can only speculate that you're having the same problem, but if you google your model type, you may find some interesting reading. And perhaps you're not alone.
Regards,
nicam49