Cannot update/install apps

Hi,
Just got a Samsung Galaxy S3. Great phone. Worked perfectly for about six weeks then Google play store died on me. I can't update apps. I can't install apps. After clicking the "Install" button, it shows the downloading bar with no percent complete or anything. It just sits there for about 5 minutes trying to download. Eventually it gives up and comes up with either error 403, 425 or 927. I've contacted Google help center and went through all their recommendations (including a factory reset) all to no avail. No I have a phone with no apps. I still have internet connection, email and everything else. I've installed Google play store from an .apk and still nothing. I managed to get one app while using wife from a friends hotspot but nothing since.

If anyone has encountered a similar problem, has suggestions or knows a decent fix I'm all ears. This is really getting to me.

Thanks in advance

 

Yeah. That was one of the first things on the Google play store troubleshooting guide.