For me, it's usually a proxy issue, and I try everything:
npm config set registry http://registry.npmjs.org/
npm config set strict-ssl false
npm config set proxy http://myusername:[email protected]:8080
npm config set https-proxy http://myusername:[email protected]:8080
set HTTPS_PROXY=http://myusername:[email protected]:8080
set HTTP_PROXY=http://myusername:[email protected]:8080
export HTTPS_PROXY=http://myusername:[email protected]:8080
export HTTP_PROXY=http://myusername:[email protected]:8080
export http_proxy=http://myusername:[email protected]:8080
npm --proxy http://myusername:[email protected]:8080 \
--without-ssl --insecure -g install