Screen Blackout on Mac Pro 3.1

This is new and I think comes with last Mavericks Update "OS X 10.9.1 (13B42)". Sometimes my Screens have a Black out and I have no control via Keyboard. So i must do everytime if this occurs a hard Reset. And there is no Crashlog that I could send to Apple. I have no Idea whats going on. It seems this happens only if I run the Programm Reason. But I could not swear on it. But this behavior is coupled to Mavericks the Problem must be there cause any Application has no direct connection to the Screens. Also my System Macpro 3.1 seems not in the Focus of Apple Development and Support. So it is very difficult to find some helpful Information. Any Suggestions or Ideas? What can be done testing around this? Sometimes it happens twice a Day. And sometimes the System run the whole Day without any Problem.