I tried your suggestion of pressing Alt+Spacebar, but no menu appeared. As usual, it happened again within 30 seconds, but still no luck.
However, I looked into the Event Viewer (don't know why I didn't think of this before) and looked at recent events immediately after my desktop was shown. My search resulted in numerous msiInstaller events. They showed 2 for the past hour, 4 the past 24 hours, and so on. I then viewed all of the events created by msiInstaller and found thousands of failed Akamai Net Session Interface install attempts. I looked at one of the failed events and, sure enough, found an identical event occur about 30 seconds after, just like the problem. The other thousand events showed lots of different times, but each with one duplicate.
Anyway, I decided to delete the Akamai Net Session Interface, since it was no use to me anyway (don't even know why I had it).
I have yet to see what happens, but for now I am convinced that the program was the problem.
Why it sent me to the desktop (showing nothing), and was done 2 times within 30 second intervals? I have no clue.