You must activate your international roamnig. Must call your operator in your country to activate it. That`s why u don't register to any networks.I have cm7.2 rc1 and im from the netherlands but now im in deutchland and i have no mobile signal what to do?
On the other side, if u search manually for networks and can't find any, then the problem is within the phone. Maybe you're in airplane mode or there is a problem with your ROM (try fixing permissions but i think no chance whatsoever).