FYI on hard shut down with the power button in Windowz XP. When you do that, Windowz thinks it's an abnormal event and therefore it does NOT save a copy of the Registry. What that means is that the "System Restore" function likely won't work if you have a problem with the system because there will be no "Restore Points" to revert to.
Each time Windowz XP boots and shuts down successfully it stores a copy of the registry in the form of a "Restore Point" which you can access in "System Restore". It will only do this if the system boots normally, runs normally, then shuts down normally via the shut down menu.