Here is what I tried. Seems to be working.
1. Either use your previously created USB recovery stick from your own
machine OR download the image from the support website. Follow the
directions on creating the USB recovery stick (quick format doesn't matter,
but FAT32 does).
2. Boot into the recovery tools using the instructions provided by
Microsoft or on this forum.
3. Select your language and keyboard
4. Press Troubleshoot
5. Press Command Prompt (I'll use CAPS for commands, but they can be in any
case)
6. Type DISKPART.EXE
7. Type LIST DISK (there's a space between LIST and DISK) (a list of your
disk partitions will appear)
7a. Type SELECT DISK SYSTEM
8. Type CLEAN (it will come back with a success message)
9. Type EXIT
10. Close the command prompt, which will return you to the recovery screen
11. Press Troubleshoot, Reset, Next (skip the recovery key is asked),
Repartition the drives, Just Remove my files (which is faster, but either
choice works), and Reset (I think I got that order right..in any case, reset
your Surface).
12. The Surface will go through the reset process.
13. A bios screen asking you whether you want to reset the TMP will appear.
You can press ESC, but the support tech said that you can also press and
hold the power button for 30 seconds to turn off the Surface, and then press
it again to turn it back on.
14. Enjoy Windows 8.1 and wait for the Consumer Preview of 10!