Getting an error "ORA-00093: pga_aggregate_target must be between 10M and 4096G-1" on Oracle DB startup
Found an answer at : http://www.databaseskill.com/400704/

But the explanation is not very clear. To summarize : 


This property 'pga_aggregate_target' is in a file called an spfile which is present at 'C:\app\dbhome\product\12.1.0\dbhome_1\database' for example.
I edited this value to one fitting the range which in my case I changed to 855638016
Further you require a init file at the same path. If one is not present at the above path you can retrieve a file from 'C:\app\dbhome\admin\orcl\pfile' and rename it to initorcl.ora 
After doing the above steps connect to an idle instance by running sqlplus / as sysdba and try the startup; command


Answered my own question for future reference