I have been pulled into a situation where a KVM server (CentOS 6.2) lost power and upon reboot one of the guests hasn't started up again (XP SP3).

I have SSH'ed in and someone must have changed something relating to the hyper visors prior to the power loss, but not rebooted all the guests. This particular guest wouldn't start because it was configured to use /usr/bin/qemu-system-x86_64 which isn't there now (assuming it was before?). I changed it to use /usr/libexec/qemu-kvm as this is what all the other guests on this server seem to be using, and its booting up.

Using virt-manager on my local machine I can connect to the display of the XP machine and it gets as far as this screen; http://support.gateway.com/emachines/issues/2-1131285152-01.gif

The problem I face now, is that which ever option I choose the machine just reboots. So it's and endless loop. I thought that perhaps a file system error maybe present due to the unclean shutdown. There is an XP SP3 ISO mounted under the guest, which I booted from in an attempt to access the recovery tools, but I don't have the Administrator password!

I am out of ideas, and it's turning out to be quite the conundrum. Should I use a 3rd party live CD to test the FS for errors? How else can I trouble shoot these restarts?