What is going wrong when Mountain Lion download does not start? I purchased Mountain Lion on App Store and start downloading. It shows an icon the the task bar and a progress bar on the Mountain Lion logo.

But it just doesn't start download. It has been one hour since it started but the progress bar is still empty.

What is going wrong?
There are two things that come to mind:


The store is so busy that it's not sending the data to your computer to start the download.
The usual things have failed and you can jump start it by following some steps on troubleshooting an App Store download.


Here are the self help steps:


Mac App Store: How to resume interrupted downloads