I believe my work proxy is preventing me from being able to add themes and packages to Atom. From the preferences menu, I get:
Fetching featured packages and themes fai
For Windows you can easily configure the https-proxy via command line:
amd config set https-proxy https://9.0.2.1:0
It should be stored under C:\Users\...\.apm in file .apmrc
See userconfig with command
amd config list