Nokia Lumia 920 not picking up 3G network

Hi guys,

I just bought a Nokia Lumia 920 secondhand and when I tested it with my MTN simcard it had 3G signal. Soon as I got home, I did a phone reset, and now it only registers Edge signal. So I know it works with 3G, but did it wipe out some settings when I did a reset?
Is there anyone who is aware of this problem, and how do I fix it? The forums online doesn't look so helpful...