if you do that, the system will power down/turn off as normal. It will not just "switch off" as it would if you unplugged it from the mains.
Why not go through the normal procedure?
I have Windows XP on my computer. What is the most horrible thing that can happen to my computer if I turn off my computer by pressing the power button on the computer and not clicking Start, Turn Off Computer, Turn Off? Also what is the percentage chance that this horrible thing will happen if I simply turn off the computer by pressing the power button? Thank you very much. user429