Freezing Windows 2008 x64bit guest

[Christoph Adomeit <Christoph.Adomeit@gatworks.de>]

Hi,

we are running several kvm servers with kvm 0.12.4 and kernel 2.6.32
(actually we run proxmox ve)

These proxmox servers are running all kinds of vms rock-solid, be it
linux or windows 32 platforms.

But one Windows 2008 64 Bit Server Standard is freezing regularly.
This happens sometimes 3 times a day, sometimes it takes 2 days
until freeze. The Windows Machine is a clean fresh install.

By Freezing I mean that the Machine console still shows the 
windows logo but does not accept any keystroke and does not answer
to ping or rdp or whatever. The virtual cpu-load is then shown
as 100% (by proxmox).

We tried several combinations of ide or virtio, several virtual network cards (intel and realtek) and single-cpu vs multi cpu. The Problem persists.

The Windows Machine is a quite fresh install but runs exchange and 10 rdp sessions.

We are experienced linux-admins but we dont find any hints on the kvm servers what might be the problem, no syslogs,dmesgs, nothing. Also there are no 
dumps on the windows guest.

Do you have any hints what might be the problem and what we could do to debug the problem and to get more information of the root cause ?

Thanks
  Christoph