If you can not login to your wordpress site using administrator account in conventional methos, then you may create another administrator account using mysql commands.
After changing hosting provider of a phpBB forum you may face few problems. You need to delete all contents of /cache folder. Make sure this folder is writable.
Your PHP installation appears to be missing the MySQL extension which is required by WordPress. Run: apt-get install php5-mysql in hosting account.
After changing hostname of your VPS, you need to restart VPS (Type sudo reboot in command line). This will solve the issue, “Unable to resolve hostname”.