SQL> select status from v$instance;, the status comes as "STARTED"
Your database is in NOMOUNT state : looks like the controlfile is not found where it should be. What is there within the alert log ?
try the following:
sql> alter database mount;
sql> alter database open;
If it returned error, send them
i was struggling to resolve these errors....
Of frusty.... i uninstalled the Oracle .. and again re-installed it... & it started working
I think something went wrong during the first installation...
but having those errors.. and solving was good learning!