CentOS virt - Sep 2011 - Second VM cannot use the network.

Hi,
  I started to use libvirt and kvm yesterday. The first VM works great.
  Today I made another VM, same configuration as before. But its
network just did not work. The guest cannot even get a dhcp ip.
  The network is NAT mode. The first VM got internal ip correctly.
  The command I made the VM is:
virt-install -nzabbix1 -r2048 --vcpus=2
-c/var/lib/libvirt/images/CentOS-6.0-x86_64-netinstall.iso
--os-type=linux --os-variant=rhel6 --disk vol=kvmguests/zabbix1 --vnc
-v --virt-type=kvm --check-cpu --prompt --arch=x86_64
--vnclisten=0.0.0.0 --noautoconsole --noreboot --autostart

  What should I do?
-- 
???????
???????