Photoshop :: PS Opens Files But Fails To Display Them

im using vista x64 and PS CS4 (updated). the problem occurs on both 32bit and 64bit versions.�when i open an image with PS (does not matter which type or which way to open it), PS seems to open the file correctly, but does not display it at all.everything looks like the image is opened (f.e. small thumb of it in the layers window and the name of it in the title bar), but where the image should be displayed in fullsize you only see the grey PS background.it seems that besides this PS works completely fine. f.e. when i use the paint bucket tool on the grey area in the middle, the layer thumb changes to the color used..another strange thing: when i switch to another program and switch back to PS the grey background is gone and instead you see whatever program is beneath PS at that moment.. you can move the PS window and see right trough it, only the PS control windows are still displayed. thats what you see in the attached image: there is no screenshot of my explorer loaded in PS,