I have a Facebook icon PNG that I want to edit to create a sprite.
But the image is distorted upon opening. Saving it gives the same distorted image. Result of opening in PS CS4 v 11.02
I see you have the image open in Index colour mode (see your Photoshop file toolbar - fb.png @ 582% (Index)). Index colour mode is a low-colour (256 colour) option that can have unexpected effects on your raster graphics. Saving from this colour profile will no doubt perpetuate any problems you are having in the Photoshop file into the exported graphic.
Try switching to RGB colour mode for this; something must have gone wrong when you opened the original .png file up, as I was able to open your attachment without any issues. Saving your .png from RGB mode should prevent this kind of problem from occurring. Oh, and make sure to save at PNG-24 and not PNG-8 when exporting!
See this Adobe page about colour modes: http://helpx.adobe.com/en/photoshop/using/color-modes.html
I hope this helps!