You need to understand when editing or correcting a digital photo is that the camera/sensor sees things differently than the human eye and brain do. The easiest way for me to explain it to people is that the sensor does not handle gamma very well and needs corrected. I know that is an oversimplification of what happens but it works. People like to blame other things and people. It make them feel better for some reason.
The very first thing I do in Photoshop if I have to work on a photo is to deal with the gamma correction either adding or taking out. I do that and correct the resulting image for any changes in exposure that need done. I use CS5 but started correcting gamma way back in the series of photoshop. The place to find it in CS5 is under image/adjustments/exposure and it is the bottom slider. Play around with it and see how you like it. It will in most cases be adding gamma. This affects the color and shadows mostly.
If you do not have Photoshop you can use some of the others to do the same or use an a simple method that works ok and that is Picasa by Google and use the shadow slider and the highlight slider if necessary and you can do pretty well with them. They are not the same as PS but they get close. I have done side by side comparisons and for the money, free, Picasa does ok with this.
Depending on your computer and settings the gamma correction on some images is not instantaneous. If you are having problems with things in PS taking a long time to process it might be that the computer is using memory for other items. You can set the amount of memory Photoshop uses under the edit/preferences/performance area. I set mine a little higher than the top of the range they suggest. It does not hurt the performance of the computer besides when I work in PS I work in PS and do not do anything else.
And with all this, if you do not calibrate your screen and work in an area that has good “daylight” the images are going to have problems when you print them matching what is on your screen. You can buy daylight light bulbs for use around the computer and for lighting props for studio shots. You can go to many places and see the difference as they usually have displays so you can see the difference.