Unity loads the wrong IDE

I have Unity set to load my code in Visual Studio 2013. For some reason, it will frequently load other IDEs. Some days, it will load VS 2012. Some days, it will load monodevelop. Today, it is loading VS 2010. Sometimes, I will get the loading screen for one IDE (mono usually) and then a different IDE will open. I usually already have another project open in VS 2013 when I open my unity code. Any ideas to get it to open properly?

I am running windows 8.1 and the latest free version of unity.

Take a look at this - http://wiki.unity3d.com/index.php?title=Setting_up_Visual_Studio_for_Unity