I have calibrated my monitor with Colorvision Spyder (Optical). Because of that, Adobe Gamma is de-installed. Until last week everything worked fine. My system was using Adobe RGB 1998 as it's working space.

Now all images being loaded into Photoshop or Photoshop Elements show a severe color cast on screen.
It doesn't make any difference which profile I select in Color Settings. Adobe RGB, sRGB or Color Match all show a severe color cast. When the images are loaded into viewers outside of the Photoshop environment (for instance ACDSee), all the images appear normal on screen.

Only when I turn color management off, the images in the browser and those loaded into Photoshop appear normal.

Does anyone have a clue what has happened to my system?

Have you checked the "Advanced" color settings in photoshop? Perhaps you have it set to automatically convert images to some other profile when opening.

Thank you Vikki, but I checked that one.

The default setting is that embedded profiles should be preserved.