In terms of troubleshooting, first check the alert log to see whether the instance even starts, or whether there are any relevant error messages in the alert log. Check your init.ora file to ensure that you do not have syntax errors or are attempting to set parameters that cannot be set for the system resources you have available. You could create a database via the Database Configuration Assistant (DBCA). This is an Oracle tool that is graphical in nature, and it will guide you through the creation of a database by first asking you a number of questions about the database you would like created, and then running the associated scripts it creates.
This was first published in February 2007