The .Net 3.5 install is an optional install found in the Turn Windows Features On or Off section of the control panel.

  1. On the Start screen, type and then choose Control Panel
  2. Choose Programs, and then choose Turn Windows features on or off
  3. Select the .NET Framework 3.5 (includes .NET 2.0 and 3.0) check box
  4. Follow the prompts to install .Net 3.5 and then reboot