By I/O card I assume you are referring to your JetDirect or the optional HP/GL2 formatter board, your EIO devices?
If you have them installed and the plotter does not recognize them.
Shut down the plotter then remove the power cord from the plotter or the wall and wait 5 mins.
Remove ALL EIO devices (JetDirect / formatter).
Plug the plotter back in and restart the plotter.
Test functions of the plotter.
Shut down the plotter and then add back only the JetDirect.
Start the plotter and check the function, and check if the menu will allow you to setup the JetDirect.
If successful, shutdown again and reinstall the Formatter Card (if you use one).
Test functions and check the I/O setup in the menu.
The idea in a nutshell, remove the cards and add them back one at a time to see which one if any is bad and causing the I/O to shut off.
If this does not help, you may need to replace the plotters Electronics module