FIXED: see this thread:
Tried twice already, still getting this: Couldn't update to Windows 8.1 Preview, Error 0xC1900101 - 0x30018.
Apparently the first part of this error code (0xC1900101) is something that many people experience, but this second part (0x30018) is something more specific. Where can we get the list of all error codes and the reasons for them?
Edit 1:
As suggested, I ran wsreset to reset the Windows Store cache, but it didn't help. As per another suggestion, my graphic card drivers are the latest from NVidia. My computer runs Windows 8 Pro perfectly fine, and there's no reason not to be able to update.
Edit 2:
During the third install attempt I noticed that it fails already after the installation itself, when it's doing device configuration. Somewhere at 65% where it says "Getting devices ready..." it throws the blue screen with unhappy smiley :(. I have a suspicion it's some peripheral device connected to my computer or its incompatible drivers, so I'm going to disconnect everything and try again.
Edit 3:
Disconnected every possible device I had connected to the laptop, removed the ExpressCard, etc -- just the bare machine, but still fails at the same place. Really upset, wanted to try 8.1 so much.