title: On PC restart, Android studio (4.0) shows all "red" for all android / java classes
body: <p>Recently restarted computer and opened up existing project and Android Studio shows "red" for all android and java classes.</p>
  
  <p>Builds fine - details below.  (Even introduced a compilation error which the build detects just fine; restore and builds OK.)</p>
  
  <p>Tried (with no effect):</p>
  
  <ul>
  <li>restarting</li>
  <li>invalidate cache / restart</li>
  <li>opened another past project which had been fine and same error.</li>
  <li>Trying to use menu "File | Settings" has no response.</li>
  </ul>
  
  <p>Thanks for any ideas...</p>
  
  <pre><code>Starting Gradle Daemon...
  Gradle Daemon started in 1 s 15 ms
  &gt; Task :app:preBuild UP-TO-DATE
  &gt; Task :app:preDebugBuild UP-TO-DATE
  &gt; Task :app:compileDebugAidl NO-SOURCE
  &gt; Task :app:generateDebugBuildConfig UP-TO-DATE
  &gt; Task :app:compileDebugRenderscript NO-SOURCE
  &gt; Task :app:javaPreCompileDebug UP-TO-DATE
  &gt; Task :app:generateDebugResValues UP-TO-DATE
  &gt; Task :app:generateDebugResources UP-TO-DATE
  &gt; Task :app:mergeDebugResources UP-TO-DATE
  &gt; Task :app:createDebugCompatibleScreenManifests UP-TO-DATE
  &gt; Task :app:extractDeepLinksDebug UP-TO-DATE
  &gt; Task :app:processDebugManifest
  &gt; Task :app:processDebugResources
  &gt; Task :app:compileDebugJavaWithJavac UP-TO-DATE
  &gt; Task :app:compileDebugSources UP-TO-DATE
  &gt; Task :app:mergeDebugShaders UP-TO-DATE
  &gt; Task :app:compileDebugShaders NO-SOURCE
  &gt; Task :app:generateDebugAssets UP-TO-DATE
  &gt; Task :app:mergeDebugAssets UP-TO-DATE
  &gt; Task :app:processDebugJavaRes NO-SOURCE
  &gt; Task :app:mergeDebugJavaResource UP-TO-DATE
  &gt; Task :app:checkDebugDuplicateClasses UP-TO-DATE
  &gt; Task :app:dexBuilderDebug
  &gt; Task :app:mergeLibDexDebug
  &gt; Task :app:mergeDebugJniLibFolders UP-TO-DATE
  &gt; Task :app:mergeDebugNativeLibs UP-TO-DATE
  &gt; Task :app:stripDebugDebugSymbols NO-SOURCE
  &gt; Task :app:validateSigningDebug UP-TO-DATE
  &gt; Task :app:mergeProjectDexDebug
  &gt; Task :app:mergeExtDexDebug
  &gt; Task :app:packageDebug
  &gt; Task :app:assembleDebug
  
  BUILD SUCCESSFUL in 10s
  21 actionable tasks: 7 executed, 14 up-to-date
  </code></pre>
  
  <p>1 of 1000s of editor "Cannot resolve symbol":</p>
  
  <p><a href="https://i.stack.imgur.com/Qdl6m.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Qdl6m.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/FRkbf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FRkbf.png" alt="enter image description here"></a></p>