Photoshop CS2 not showing true colours.

I've been using it like this for some time but the more I do, the more annoying this gets.

At some point, not sure when, and no idea why, my Photoshop stopped showing the real colours of images opened in it. I can view the image in IrfanView (the viewer I use) or any other application where it displays correctly and then open it in Photoshop and it will have this brown tint to it. The colours just aren't the real colours of the image for some reason. Take an image, desaturate it and instead of a real black and white image it's partly brown.

Has anyone ever encountered this? I've dug around in the colour settings but that didn't help any. It's really starting to frustrate me. >.<

We had a similar problem on the computers which ran CS2 at school. It would appear fine on the screen but would print everything with a yellow hue. If I remember correctly the uninstalled then reinstalled it whenever that happened.

I would seek a second opinion before doing it though, I'm fairly hazy on this.