I was trying to run MongoDB:
E:\\mongo\\bin>mongod
mongod --help for help and startup options
Sun Nov 06 18:48:37
Sun Nov 06 18:48:37 warning:
Create the data/db directory in your main (windows) partition:
C:\> mkdir \data
C:\> mkdir \data\db
and then go to your mongo_directory/bin and run mongod.exe:
C:\> cd \my_mongo_dir\bin
C:\my_mongo_dir\bin> mongod
DON't CLOSE THIS WINDOW
Now in a different command prompt window run Mongo:
C:\> cd \my_mongo_dir\bin
C:\my_mongo_dir\bin> mongo
(REMEMBER YOU HAVE TO KEEP THAT OTHER WINDOW OPEN)
This solved the problem for me.