I'm having problems getting Docpad to run on Windows.
I did the following.
I got an error message that said 'docpad' is not recognized as an internal or external command, operable program or batch file.
Maybe I'm missing a step somewhere? I've also tried submitting the command to the node command prompt, and have also checked the troubleshooting guide and done a general google search.
Unless you installed an NPM module with the -g option (which is not indicated in the docpad web site so I suspect you didn't) the module won't be available on your PATH.
You can still run it by indicating the full path, for example run the following from the folder where you ran the npm install command:
node_modules\.bin\docpad.cmd
I had this same problem and a restart didn't help me.
What worked for me was installing via the 'nodejs command prompt' rather than the standard windows one.
I ran npm install -g docpad then navigated to my empty folder and ran docpad run and it worked straight away (after 1 hour messing around with the windows command prompt).