Visual Studio tracks the state of projects and files in a solution (e.g. files left opened when Visual Studio solution was last closed) in SolutionName.suo file. Over time this file can get big and corrupted. Once this file gets corrupted, Visual Studio can hang when the corresponding solution is re-opened. To get around this problem, simply delete the .suo file and reopen the solution.
Note: The .suo file is a hidden file. You would need to show hidden files in Windows Explorer to discover and delete this file.
