Hi James,
Just a quick question have you upgrade the DB or installed any new DB patche set during the installtion. In that case you need to go for an startup upgarde.
Then run below commands:-
STARTUP UPGRADE
@<oracle home>/rdbms/admin/catupgrd.sql
SHUTDOWN
STARTUP MOUNT
ALTER DATABASE OPEN RESETLOGS;
Also can you paste the Alert_SID.log file here for the latest error.
Let us know if this helped you.
regards,
Ram