Or you can install manually. Hit Windows key-R and enter "appwiz.cpl" without quotes, then click "Turn Windows features on or off." .NET 3.5 should be at the top of the list. If the box next to it is empty, click it to install, and when it's finished, restart your computer. If the box is filled, that means it's already installed. Click the box to uninstall, restart your computer, then install is as above and restart again.