First of all run emacs with --debug-init from your terminal and check if complains about being unable to verify the elpa archive due to an invalid key. If that is the case, copy the public key displayed to you.
I ran into this problem because the GPG keys used by the ELPA package manager to verify authenticity of packages downloaded from the GNU ELPA ...
If you try to install the package gnu-elpa-keyring-update (which seems to have the purpose of updating the keys used by the package manager), you will see in its description that you can do:
gpg --homedir ~/.emacs.d/elpa/gnupg --receive-keys 066DAFCB81E42C40
on the commandline to get new keys manually. To make sure you are asking for the correct key (...
You may have to just use http instead of https
Here is what I have (essentially removed the s from https)
Not the perfect solution but something to get me going.
(setq package-enable-at-startup nil)
'("melpa" . "http://melpa.org/packages/"))
'("gnu" . "http://elpa.gnu.org/...