Whenever i press Ctrl+S from keyboard or whenever i click on any file in Solution Explorer it automatically opens output window only in Visual Studio 2012.
I tried
Tools > Options > Projects and Solutions > Show output window when build starts
I am using Visual Studio Professional 2012
But its just not working. Its irritates a lot. Please suggest how to get rid of it.

if someone is facing this issue in visual studio community 2015, in my case the issue was caused because of the use of Backup and sync utility from google, I have synced my source directory to my google drive to maintain the latest copy of source backed up.
The backup utility locks the file which you might be editing for syncing it to cloud storage. since the file is locked by another process, the visual studio cannot save the changes in the file.
The fix was to pause the syncing for the time you are doing frequent changes. In your case, it might be some other process which might be locking the file.