'''++Vincent Gnapi++''' a bad battery should not be the issue if you have power coming from your AC adapter. I would definitely go ahead and replace the battery but be prepared to further troubleshoot after. It is possible that this is an issue with the DC in jack. Since the computer has been off for years by now the battery is discharged below it’s threshold to accept a charge. So, first new battery then consider checking the DC in jack to make sure that your computer actually gets power.