title: Visual Studio is acting weird. How do I fix this?
body: <p>My installation of Visual Studio was fine previously, but has started acting weird lately.  Some of the symptoms include</p>
  
  <ul>
  <li>Visual Studio randomly hangs or crashes</li>
  <li>Visual Studio won't start</li>
  <li>Intellisense disappears sometimes</li>
  <li>Plugins are not working, or are failing to start</li>
  <li>I can't install or uninstall tools</li>
  <li>I can't connect to source control anymore</li>
  <li>Certain known good project types fail to load properly</li>
  <li>Known file types don't have syntax highlighting anymore</li>
  <li>I can't add files to a solution because the option is greyed out</li>
  <li>I can't add, remove, or update files to a solution due to an error</li>
  <li>I can't add or remove projects to a solution due to an error</li>
  <li>I can't open a solution due to an error</li>
  <li>The debugger cannot launch, or attach to processes</li>
  <li>I can't find any templates when I try to add a new item</li>
  <li>I can't copy/paste due to an error</li>
  <li>A DLL required by Visual Studio is missing or corrupt</li>
  <li>Menus are suddenly empty</li>
  <li>Something that I know <em>should normally work</em>, now <strong>does not work</strong></li>
  </ul>
  
  <p>How can I fix this?</p>
  
  <p><sub><sub>(This question is meant to be a canonical close dupe for these types of questions)</sub></sub></p>