Downgrade from 3.1.2 to 3.0 and getting error

I currently new to WordPress, I install WordPress directly through GoDaddy and it was simple. However I purchase a template from TemplateMonster.com and the template was only compatible with WordPression version 3.0 so I downgraded. However, when I changed the files I keep getting the same errors
—- One or more database tables are unavailable. The database may need to be repaired. — I click the repair button nothing happen —

Can someone please assist?? ??