Here's my suggestion...
Click on "Start", move your mouse to "All Programs", and find the listing for DOSBox .73. Roll your mouse over that listing, and when the new menu comes up, roll over to "Configuration". You'll see an option called "Edit Configuration". Click on that, and there's your config file. Make your changes there, and then save it. That's pretty much a sure-fire way to make changes that'll stick, as I've never had any issues with changing it there.
Unless that's what you're already doing. In which case, you might want to try a reinstall of DOSBox. Something may have gone horribly wrong during your tinkering.