Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
It sounds to me as if your father-in-law might have had to reset the router, in the course of trying to get the wireless connection of the stereo working.
In which case, your printer's print-by-wireless configuration is now pointing to a 'dead letter' wireless address on your local network.
(The best way to check on this is, to see if you can still connect by wireless to your local router. If that proceeds without problem, this is not likely to be the problem. A reset of the local wifi router's settings would disrupt not only the wireless printer configuration, but also any wireless connections. For reasons too long to explain...)
If that isn't it, then you might still benefit from doing an uninstall of your MF3800 or 4800 printer's configuration from your computer, then restarting the computer, then re-installing the MF3800 or 4800 printer's drivers onto the computer.
If you need details on how to go about that, or if the former guess turns out to be correct, let me know, and I will instruct you as appropriate and as needed.