Help! Can't sign in to google

Hi,

I'm unable to log in to my google account on my phone. Over the last week, I've been having persistent sync issues with google inbox and I noticed other sync issues on the sync screen. I assumed it was something to do with the phone software so I've factory reset. However, now I can't log in at all. I have tried two accounts and wifi and 3g.

My phone goes to the checking info screen and then I get the
Couldn't sign in.
Can't establish a reliable connection to the server.

Any suggestions? The phone's a OnePlus One running the lastest official Rom.

Thanks
James