Shift to hand tool with space bar

I have Photoshop CC on a Mac running Mavericks, 16 gb memory.

While working on an image, the space bar stopped calling up the hand tool while depressed. I tried quitting Photoshop, no good. I tried restarting computer, it worked, for a little while, then went away again.

Is this a Photoshop issue, and how do I fix it? Or is it a Mac issue?

Thanks!