photo shop suddenly won't display on a 2nd monitor. Other programs do. It's not the monitor, swapped it out and still have the issue. This is on a Macbook pro running Maverick. The same file works Ok on a PC running windows 7 with a 2nd montior.
Seems to be a new bug with photoshop and Mac.
Anyone have ideas?
That sounds like one of the known driver bugs in MacOS 10.9 that hasn't been fixed yet.
Have you tried disabling GPU image drawing in Photoshop's preferences and restarting Photoshop? That might work around the driver bug.