High cpu on the process quemu-kvm on physical machine



we have a physical server with CentOS 6.4 with kvm installed on it. (hp proliant 350 with 20 Gb of RAM and intel Xeon-R)
We have diferent guests on that one. Some linux (Centos and Debian) and Windows. (2008 Server)
The linux guests are ok, but on windows machines we see a constantly high CPU usage (120- 180%) on those process with a top even when nothing is being done, and other process are ok.
We have tried changing drivers to virtio , and the result is the same,

We have no idea how to solve it.
Has anyone got any idea?

thanks in advance.