I have used premeire cs5 and cs6 and never had this issue
I just bought a new mac pro and installed the trial of Premeire cc 2014
I import clips like normal, set my sequence and the play button does not work
in the viewer or in the timeline. Can seem to make anything work
also I am on 10.9.5 which from what I can see should be fine.
Try this: create a new user with Admin privileges and see if you can get Premiere Pro to playback video once more.
THAT DID IT!!!!!
Cool news, Ernie!