Screen Scrambled, System Unresponsive

Hi,

Since upgrading my Mac Mini (2.26 GHz Core 2 Duo, 8GB Ram) to Mountain Lion, from time to time, without any apparent reason, my screen gets distored/scrambled and both the mouse and keyboard rendered unresponsive.

I then have to ssh into my Mac and shut it down.

Upon firing it up again a kernel panic is reported, and some kind of infinite restart loop is being entered, which I only can break if shutting it down via the power button, and subsequently resetting the PRAM.

When looking into the logfiles nothing out of the ordinary can be found, only when--from time to time, unforeseeably--a crash report is being created and sent to Apple, some hint on "xen" and "net6" is being displayed (I've got 12 virtual ethernet adapters configured).