I just added a Dell P2715Q monitor to my Dell XPS 8700. The NVIDIA GeForce GTX 745 graphics card doesn't have a DisplayPort output, so I am running it through an HDMI cable, at 4K and 30Hz refresh rate. The monitor looks great, but Photoshop CS5 freezes as soon as I open it and put the image on the new monitor. The menus all freeze and I have to open the Task Manager to force it to close. Photoshop continues to work as normal on the old monitor, a Dell SX2210, running off VGA.
I am stumped. I don't want to buy a new graphics card if that won't fix it. The computer has an onboard DisplayPort, which is disabled with the NVidia card. The card otherwise runs the new monitor, and other software behaves normally. It seems to be strictly a Photoshop problem on the new monitor.