You might consider finding a second Classic-or-later compact model of Macintosh that is working and for sale, buying it secondhand, and swapping the hard disk from the inoperative computer into the operative one, then backing up all the data into a third (more contemporary model of) computer with a more contemporary release of the accounting software (if any, uh oh). If the sick Classic still has a working hard disk it has been working on borrowed time for a decade or more.