In your admin panel under miscellaneous->advanced, you have an option at the bottom of the page to restore all settings to their defaults. This will delete your settings table and replace it with what a new install would give you (without damaging any of your other tables).

Sometimes, you may be playing with a bunch of settings changing their values. A few minutes later you notice something has gone wrong and your site isn't working correctly. You're pretty sure it must be due to one of the settings you changed, but you don't have any idea which setting that would be. In this case, you may find it desireable to reset all your settings to the defaults so that you can eliminate the misconfiguration and start over more carefully.