I have a PowerBook computer with a single printer/modem port and I cannot print to my serial printer. What are the troubleshooting steps necessary to isolate this problem?

1. Check all cabling and print a test page on the printer. Verify that the cable works (or has worked) with other computers.
2. Make sure that Appletalk is inactive in the Chooser.
3. If the driver has a selection for printer or modem port (Apple drivers do not but Hewlett-Packard drivers do), it usually works better if the printer is asked to go through the modem port rather than the printer port.
4. If you are using an Apple printer, make sure that you have not installed old drivers onto a newer PowerBook. Most of the drivers you need are already pre-installed on your PowerBook, and installing the older printer software can cause problems. Most of the Stylewriters introduced before the Stylewriter 1200 will run off of the Stylewriter 1200 driver. Newer StyleWriters will run off of either the 2400 or 2500 drivers.
5. If you have any third party fax software make sure it is not set to receive. This can often confuse the printer software and generate "port in use" errors.
6. If the computer has an internal modem, make sure that the modem (or Express Modem) control panel is set for internal.
7. If the software seems to be properly configured and functioning, and Appletalk is off, then the next step is to reset the PRAM. Please note that on PowerBook 5300/190 and newer models, successfully resetting the PRAM after a shutdown will put the computer to sleep. You must use the reset button to restart after that. Also note that resetting the PRAM will turn Appletalk back on (its default position) and this will need to be turned off again before trying to print again.
8. Run Disk First Aid to check for hard drive corruption. Allow Disk First Aid to perform the software repair if necessary.
9. Rebuild the Desktop.
10. Try running with the standard system extensions (plus any necessary third-party printer drivers) only. If this works then you probably have an extensions conflict.
11. Uninstall and re-install the printing software. If you are using a third-party printer, check and make sure the latest version of the printer driver is installed. If not, contact the printer vendor.
12. Do a clean install of the system software.

If none of these steps resolve the issue, you probably have faulty hardware.