title: Gradle not syncing after update
body: <p>I was working on a project in android studio. Unfortunately, my harddisk started giving errors, so I backed up my project. Then, I bought a new harddisk and installed android studio(ver 3.0.1). I don't clearly remember the previous version of android studio that I used but I guess it was 2.6. Here comes my problem. When I started to sync the gradle,it gave me these errors.</p>
  
  <pre><code>Error:Could not resolve all dependencies for configuration ':app:debugRuntimeClasspath'.
  Could not determine artifacts for com.android.support:support-core-ui:25.4.0
  Could not get resource 
  'https://maven.google.com/com/android/support/support-core-ui/25.4.0/support-core-ui-25.4.0.aar'.
  Could not HEAD 'https://maven.google.com/com/android/support/support-core-ui/25.4.0/support-core-ui-25.4.0.aar'.
  Connect to maven.google.com:443 [maven.google.com/216.58.221.131] failed: 
  Connection timed out: connect
  Connection timed out: connect
  </code></pre>
  
  <p>Then I opened another one of my projects I got this error:</p>
  
  <pre><code>Error:Connection timed out: connect
  </code></pre>
  
  <p>I searched a lot and many are suggesting solutions related to setting a proxy and some are saying that the download repository is corrupted. I re-downloaded the repository but no luck. I used an external proxy software but still no luck.
  What could be the problem?</p>