ORA-01034: ORACLE not available
dbstart will only start databases that have the third parameter in the oratab file set to Y. Check the value in that file.

You also don't need to pass the ORACLE_HOME as an argument; not sure if you actually meant to pass the SID, but anyway, the home is taken from the oratab too.

The script itself says that it should only be executed as part of the system boot procedure, e.g. from a script run during boot from an /etc/rc*.d directory. The $ORACLE_HOME parameter that's passed in is only used to start the listener; the home for each database is taken from oratab.

According to the documentation, dbstart is deprecated in favour of Oracle Restart (in non-RAC environments) in 11g Release 2; I guess that means you should use crsctl start has to start the listener and database from then. That also uses the third oratab value to decide whether to start the database.