You should NOT (I repeat, NOT) operate the Mac OS when it's warning you that you're running out of disk space. You risk data corruption and the OS behaves very strangely. This could easily account for the problems you're having. Tell your husband to remove or back up unneeded data ASAP.
If that doesn't fix your problem:
Yes the file is invisible to the Finder, so you cannot see it that way. You need to use the terminal to remove/rename it.
Open /Applications/Utilites/Terminal, (I put this in code tags because it's a longish line) type:
sudo mv /Library/Preferences/.GlobalPreferences.plist /Library/Preferences/GlobalPreferences.plist.BAK
Now enter your admin password when prompted. This will rename the file. Now restart the computer and see if the print issue is fixed.