Have had a charging issue as well, and solved it.
my SGN was not charging at all not even when turned off, started two days ago, the first evening it was only charging on one out of my three USB cables (each cable has its own wall charger).
Also my PC with "Win 8 Pro" was not recognizing my phone at all.
My first try was a bit stupid, but it worked, well for one day only. I bite on the USB cable, so the part that goes in the phone was a bit deformed, and the SGN was charging again. \o/
Next evening, I had the same problem again, but this time, non of my three cables was able to charge, even after further deforming tries.
My final solution
was to use a needle, stick it in the USB port on the phone and bend the small "tongue" a bit up, so it was exactly in the middle.
My Phone was off and the battery removed. I put all together again and plugged the USB cable back in, it started charging while off.
Then I just turned it on, after booting was almost done, my PC told me that my SGN is connected and it was still charging.
I removed the cable, plugged it back in, several times, also on all three charger with its cables, finally my problem seems to be resolved.
btw. My SGN is from November 2011, so one of the first here in Europe.
I hope this can help some other with the same problem.
Kind Regards from Germany,