After setting up MongoDB service on Windows Server 2008 R2 this error was raised.
C:\mongodb\bin>net start MongoDB
The Mongo DB service is starting.
The Mongo DB service could not be started.
A system error has occurred.
System error 1067 has occurred.
The process terminated unexpectedly.
The error came from an unclean shutdown detected.
Please visit http://dochub.mongodb.org/core/repair for recovery instructions.
a few steps will fix it (as it's written in the link above):
1) remove the file /data/db/mongod.lock
2) run mongod.exe --repair
3) start the mongod service net start MongoDB