Chrome's Developer Tools, Safari's Developer menu or Firefox's Firebug would be the best resources to start debugging.
The JavaScript Console would detect JavaScript errors or conflicting versions, usually raising "uncaught exception" errors.
Setting breakpoints to evaluate the executtion setp-by-step and inspecting the values being assigned to variables is an extremely powerful resource.
The debugging tools are valuable if, as the linked article advises, you are a proficient developer. The good news if you are not: you can still embed you Marketo Forms on non-Marketo Landing Pages, including Contet Management Systems such as Drupal or blogging platforms such as Wordpress. The solution is simple: place the Marketo form on a landing page just enough to host the form and then
put a Marketo Form on a Non-Marketo Page Using an iFrame