KVM Guests not booting
In order to connect to the serial console, you need the guest to support it first. This means the guest must have console=ttyS0 appended to the kernel start line in grub.conf. This also means the libvirt config for the VM should contain the following:
<serial type='pty'>
<target port='0'/>
</serial>
<console type='pty'>
<target type='serial' port='0'/>
</console>