Hi,
The resolution for this has been posted many times - that's what the search functionality in the forums is for.
What you have done is run Alfresco from a different location to a previous attempt, so that the db is populated but the location to the alf_dir has changes because you haven't set it to be an absolute path.
The simplest thing to do is:
1. Edit 'custom-repository.properties' in ..tomcat/shared/classes/alfresco/extension and set 'dir.root' to an absolute path.
2. Drop your db contents, and delete any existing alf_dir contents
3. Restart alfresco
Hope this helps,
Steve