To install, I downloaded the program and extracted the .zip into C:\CumulusMX\. Then, as directed by the Cumulus popup, I entered localhost:8998 and answered several pages of questions about my preferred settings and my weather station (Davis VP1). I then, as you point out, I messed up by restarting the PC rather than restarting CumulusMX after reading the restart instruction in the popup.
Now, when I try a soft boot (Ctrl-Alt-Delete), I see a popup on the lower right of the screen indicating no signal detected. I don't know what that means, but I assumed it meant that no data was on Com6 (the USB port where the USB to Serial adapter provided date to VWS). After the no signal popup closes, I see a blinking cursor towards the upper left of the screen. F8 after either a soft boot or after unplugging does not cause the PC to safe boot, just the blinking cursor.
Any suggestion would be most appreciated.