You page rank should not be affected by switching hosts. However, as that switch will also necessitate the change of your domain name’s nameservers, the resulting DNS propagation period may result in some slight inconveniences for search engine bots. In order to avoid them, simply make sure, that your website on the previous server has not been taken down, before search-engine bots start indexing your website on the new server. This should be easily apparent by the access logs on your new server.