I've inherited old CiviCRM data from a Drupal install - how do I get upgraded and running in Wordpress?
If you look in the database, check the civicrm_domain table and see if there is a value in the version field. (If there is more than one record in this table, you are dealing with a multi-site).

Just guessing, but one problem you may run into is that the original database wasn't on Wordpress. Do you know what CMS it was running on? 

(e.g. Drupal upgrades support all the way back to v2.2, but Wordpress upgrades start with v4.1.)

So one approach would be to set up Drupal on a development server, upgrade CiviCRM on this Drupal installation, and then move the updated CiviCRM database to Wordpress as outlined in this StackExchange Q&amp;A.