Re: ORA-01102: cannot mount database in EXCLUSIVE mode

Faced the same issue just now... Here's what you do:
First at command prompt check:

ps -eaf | grep smon

You would definitely find 2 entries for the current database...

Export ORACLE_HOME,ORACLE_SID, login to SQL and type:

shutdown immediate

Then logout of sql and again grep for smon... Kill that particular process using kill -9

Then login to SQL and type:

startup

The database would surely startup now.. Try and let us know!