Why doesn't my installer work?

I encountered a strange error last week, while setting up a virtual machine for some testing: Double clicking the Sitecore 7.2 installer would show the "Extracting" dialog, but after a short while it would vanish and nothing else would happen...

You'd see this: (with the progress bar animating)

And then the dialog would disappear. No obvious event log errors, no processes left running, (most importantly) and no install of Sitecore.

This confused me, so I spent some time Googling to see if anyone else had seen the issue, searching logs for errors and even using Process Monitor and Process Explorer to see if I could spot what was going on. It had to be a software compatibility issue, I assumed. Something I'd installed on the VM was conflicting with this version of Sitecore? Well, no – it turns out that wasn't the case at all...

The thing that finally let me work out what was going on was trying to extract the MSI file from the .exe:

Opening a command shell and running the .exe with the switch /extractcab threw up an error saying that the file was corrupt. So all my confusion stemmed from the problem that when you double click the .exe, this error is not shown to you...

When downloaded a new version of the installer from SDN and tried again, everything installed fine.

So it turns out that extracting the MSI is actually a helpful diagnostic test, if you're having unexplained installer issues...

I'm blaming cosmic rays for this one...