Photoshop Levels not working properly...?

I recently installed Photoshop CS3 onto my laptop, which also has Photoshop 7. The Levels used to work fine in PS7, but since I installed PS CS3, the Levels function does not seem to be working properly in both programs.

What happens is, for example, I'm trying to make a starfield (using a black backround, making Noise, then using Levels to get the right brightness proportions). However, when I use Levels to cut down the noise a bit, the preview will appear the way I want it, but once I hit 'OK' the image layer snaps back to the way it originally was with tons of noise, except that ALL the noise is exaggerated/brightened, etc.. It's like the Levels function isn't even working.

Any idea what might be causing this? It doesn't make any sense.... Thanks!
John

John,

First: while editing, do you view the image at 100%? Particularly noise is hard to judge at anything under 100% because things that have a size of one pixel then tend to not get mapped in a preview.

Then, when you talk about Brightness, I would use Curves, or at least the middle (Gamma) slider in Levels.

The end sliders in Levels clip the ends of the histogram.

Rob