What is the best way to start from scratch? I have a drupal 7 instance at work, and one at home. I added content to both sites BEFORE installing the "menu breadcrumbs" module. On my Drupal instance at work the breadcrumbs don't work properly (they are skipping a level etc) while on my drupal instance at home, the same module works perfectly.

I've already tried uninstalling, and then reinstalling the module on my drupal instance at work, but didn't have luck getting it to work. Still skipping the breadcrumbs in between. What is the best way to fix this on my work instance? Should I delete all the content? If so, how? Is this likely to make any difference?
This question is difficult to answer. Check your Drupal versions first, 7.xx, etc, i.e., if you use 7.18 at your home, the same version should be used at your work.  

If the versions are same and you still encounter the problem, I would do personally this by copying everything from my home instance to my work instance.  


Copy the whole drupal site folder to my work PC.  
Dump the database via phpMyAdmin (including DROP TABLE IF EXIST statements) and import it to my work PC. As a side note, I normally export cache tables with structure only in a separate dump file for the sake of smaller dump file.


That should be fine. This is the usual way I do for site cloning.