I keep having trouble with IntelliSense breaking in Visual Studio 2012! I'll be working just fine, then suddenly I get no dot completion on anything. It's pretty annoying, so I scoured the web to find a solution. I finally did! Here's the solution, taken from haneycodes.net:
1. Open the start menu and type “%AppData%” and press enter to get to your Application Data Folder.
2. Either you were automatically placed in the “Roaming” folder or you weren’t. If you weren’t, go to the “Roaming” folder.
3. Open the “Microsoft” folder.
4. Open the “VisualStudio” folder.
5. Here you’ll see a folder titled “11.0″ (the VS 2012 folder) and probably also “10.0″ (the VS 2010 folder).
6. DELETE (or rename) the “10.0″ folder. Note that you can now kiss your Visual Studio 2010 settings and preferences goodbye (your projects will be safe and sound).
7. DELETE (or rename) all other folders that are not the “11.0″ folder, assuming you used to have Visual Studio 2008 or whatever.
Now restart Visual Studio 2012 and you should be good to go!