Since I upgraded to Mavericks when I open a powerpoint in Slideshow mode my screen goes black and it restarts Powerpoint. Anyone know how to fix this or experiencing this yourself?

This is an answer!

Just update your office! It will work! I had the exact problem after upgrading to Mavericks.
 

Try to update your powerpoint with Microsoftupgrade > Mac HD/Library/Application Support/Microsoft/MAU2.0

(suggested by Agustin) It works!