It says "No Solr instance available when trying to clear the cache", should I reinstall that module?
First check whether your solr instance working properly or not. Goto http://localhost:8080(your port)/solr/admin/.
And in your site goto admin/config/search/apachesolr/settings/solr/edit page and enter SOLR SERVER URL and click on test connection whether your solr instance working or not. If not try to re-install solr if there is not indexing.