A MiKTeX installation should do it but can you check for sure that fancyhdr is there?
IIRC, it is not in the standard TeXLive installation and while I have it now, on my original installation 6--7 years ago I had to install it separately. Now, when setting up a new computer, I say the heck with diskspace and download everything.
Do you still have Tinytex installed? If so, can you be sure that you are compiling with MiXText? I am a Linux user so I have no idea how Windows will handle things.
The other thing, you could post a cut-down copy of your .rmd file and someone can have a shot at running it. I can give it a try but even better would be another Windows user.
Good luck.