When good CONFIG.SYS files go bad

At home, I'm the chief technical officer of the establishment. Somebody has a reasonably recent laptop, but I don't like laptops. Laptop screens and laptop keyboards are two arguments in favor of the desktop where a laptop isn't needed. The home desktop is from early 1998. For a week it has been loading Windows successfuly only about one time out of three. The problem occurred after removal of a McAfee antivirus program that came as software from the OEM when the computer was new. Since it became impossible long ago to update the definitions without spending some bucks, Grisoft's free AVG has been doing all the antivirus work for a long time. McAfee had its tentacles into everything and even its own uninstall program did not remove every last vestige. I finally realized that there was something seriously wrong with config.sys. This did not happen to be one of the files backed up, needless to say. Whatever was wrong was causing everything to hang up with a flashing cursor. I couldn't even reboot or turn things off, but had to remove the power cord. Config.sys is working and is now backed up. So there's no need to recur to the laptop and no need to invest in a new desktop. At least for now. Mirabile dictu! I thought it would turn out otherwise.