Dear all:
I ust installed Fedora16Fedora16 X86_64 on my new machine, and then I ran the commands as follows(ran as root):

yum install qemu-kvm
yum install qemu
yum install libvirt
yum install virt-manager

then I started the libvirtd as follow:
/etc/init.d/lbvirtd start

So , it ran well.

However, after a few days , when I ran the command "virt-manager" , it showed as in the attachment.

it seemed that ti cannot connect the hipervisor.

Then I did a little test:
I ran the conmand "virsh list" , but it didnot work,either.

Then I used Python as follows:
import libvirt
cc = libvirt.open(r'qemu:///system'

)

but it didnot work,either.

All the test above are under root . I hope that someone can give me some suggestiion. Thanks to all!