This may sound really basic, but check your monitor cable and connections. I've had that happen when a connector got loose; apparently where one of the signal lines was the first thing to disconnect.
If it's not everything on the display that's gone wonky, but just the images inside Photoshop, have you done anything (or downloaded any OS updates) that could have affected the monitor profile that's associated with your display at the operating system level?
It might be a good idea to describe your system (OS version, video card, monitor model, how it's hooked up, etc.) to get more specific suggestions.
Thank you so much for your quick response. I have checked the monitor connections and they seem OK. I have not downloaded any OS updates recently other than CS4 but only subsequent to the problem occurring. I had an IT specialist here earlier who loaded a new graphics card but that made no difference. An interesting aspect is that my screen saver still has perfect colours as do any internet pictures I download. While Photoshop is affected I also run Nikon Capture NX and that also has the same distortions. As I open a file in Bridge you can see the photos are displayed normally for an instant and the green hue cascades down all the pictures before you can open any single photo – very weird.
My system is as follows:
64bit operating system
Installed RAM 16GB
Processor Intel (R) Core9TM) i7-2600CPU @3.4 GHz
Any ideas would be most welcome
Since my last communication with you I had even loaded CS6 on a free trial basis and the green hue was there too so I had nowhere to go! I have now had an expert actually on site look at the problem. He was most intrigued by the green hue and we checked whether the green hue occurred in Paint but the colour was perfect as it was in other Microsoft applications. We then checked the printer and that worked perfectly with no green hue even though the green hue was apparent on the screen when the print was requested. He then went onto a site: www.gballard.net where the exact problem was described very explicitly. It seems that the monitor settings had been inadvertently changed somehow and this throws Photoshop (I had recently cleaned the screen and the adjustment keys are flush with the screen so I guess I had not noticed any random changes. I believe I would have noticed something was wrong had my screen saver been distorted.) The distortion only appeared subsequently through Photoshop. What made it more difficult to find was that when I tested another monitor the green hue was the same as my screen so I assumed the monitor was fine. Even when we changed the monitor back to Factory Settings, the process which in the end rectified the problem, the picture stayed green until we had actually closed the file and reopened it and only then was the colour correct.
I am hugely relieved and very appreciative of your rapid response when I was feeling somewhat desperate!
What you're describing just sounds like the display profile is wrong or corrupted.
Change the display profile in the OS settings to the profile supplied by the display maker, or fall back to sRGB or AdobeRGB (whichever is closest to your actual display).
You have to watch your windows updates or they'll (microsoft) try to sneak in some generic profile for your monitor.