Some HP computers have a built in support function that is activated by pressing ctrl alt s
The conflicts with a Blender hotkey (for scaling armatures).
Having some other process or program (window manager, operating system, mouse driver, and so on) eat key press or button events before Blender sees them is not uncommon. The fix is either to change them in the offending program or if you are using Blender 2.57, change them in Blender's User Preferences. Yes, hot keys are configurable now. Woo woo!