Default no signal on G zones. Just on 3G zones...

I was downloading a file on my TYTN from the microsoft site "framework 2.0"-something... using the phones network GPRS on "G" mode. The download took a long time and then it blocked the device. After a soft-reset, I could see the signal bars, but no "G" sign, just a "no connection" sign. Can't do/recieve call, sms or gprs... When I enter a 3G zone, all comes back to normal. But in G zones my phone is useless.
But if I'm on a 3G zone, and I chose the phone option to just use G, it connects fine! the G sign appears and I have no problems.
I upgraded to the last radio version, upgraded to WM6 and the trouble continues.
about 2 months ago I had a broken screen and change it myself. The phone worked fine for I month after that, I think it's not related but I opened the phone again just to see if I could had done something to cause this, but saw nothing wrong or burnt.
My phone had original rom with WM5 when the error appeared, so it wasn't a flashing error. As I said, installed WM6 and the latest radio version and problem persists.
I've searched the forum and found nothing like this, can someone help me?
Thanks.