Could be that you have expired Google certificates on your machine. Google Internet Authority G2 certificate seems to be a common one that recently expired on users machines and is causing this problem.
Debug log will show:
ERROR: Unable to download webpage: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)> (caused by URLError(SSLError(1, u'[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:590)'),))
To check for expired certificates:
1. Open the certificate manager - certmgr.msc (Start > Run)
2. Action > Find Certificates.
3. In the Contains field type 'google' (without quotes), and change Look in Field to "Issued To"
4. Delete any expired certificates.
You can download new ones from here: