>'/sbin/ifconfig -a' returns:

>lo              Link encap:Local Loopback

Your system is not seeing your network cards. It is only seeing your loopback device.

I opened system->administration->network->edit->hardware device, and deleted the mac address from the box, and pressed Probe.

In less than 1 second it gave the correct mac address in the box.

Probe is not the reason your system has no network. What else did you change?