GPS never gets any signal at all on Galaxy S3

So I tried using navigation on my AT&T Galaxy S3 phone the other day, and to my surprise, I found out that the GPS doesn't work at all anymore. It get 0 signal. It's just completely useless. I have tried several things to make it work, but so far, no luck. Here are the things I tried so far:

- Rebooting the device;

- Battery pull;

- Downloading an app called GPS Test that "clears" the GPS cache (A-GPS XTRA Data) and Downloads it from the internet;

- Tightening the screws on the back of the device, especially the one next to the GPS antenna;

As I said, none of that helped at all. Everytime I try using the GPS it just stays stuck on "Searching using GPS...". Any GPS test apps detect 0 sattelites; there's 0 signal. The phone is using stock AT&T 4.3 Android. Now I don't know if this is a hardware or software issue, and that's what I'd like to find out. Are there any tests that will tell me for certain if this is a software or hardware issue? Or are there any useful tips anybody can suggest?

Thank you in advance.