Don't know what kind of power supply Gateway uses, but had similiar problem with grandsons computer few months ago.
AT type PS's have a mechanical off-on switch. They physically connect and disconnect the ac pwr, same as a wall switch for your lights. If the pwr switch on your computer happens to be in the on position when you plug the power cord in to the ac outlet, the computer will come on.This is known as a "Hard" switch.
However-
If your computer has an ATX type power supply, the ac power is controlled by a chip on the mobo.One side of the computer pwr switch is connected to grd, the other side connects to the pwr control chip on the mobo. When you press the pwr sw in this instance you actually put a grd (a "0" or Lo) on the pwr ctrl chip and it in turn switches the ac pwr on or off. This is called a "Soft" switch.Thats why ATX pwr supplies have a standby pwr lead. If you look on the side of the pwr sup you will see a lead 5vsb.

If you have an ATX board, you have probably got a bad mobo.This is what happened with my grandsons computer.It appeared to operate normally except if you shut it off and pulled the power plug, when you plugged the pwr cord back in, the computer would come on by itself w/o touching the power swith.In troubleshooting the computer, I checked several of the regulator transistors on the mobo and found a couple of them shorted. I called MSI support and told them the symptoms and what I had found, they said the board was bad and sent me a new board. That took care of the problem.
If you get a "It's safe to turn your computer off" msg at shutdown, you probably have an AT supply, If the computer shutsdown on it's own, you have an ATX pwr supply.
Hope this helps.
John

On Sat, 24 Jan 2004 22:09:09 -0500, Merrill Wymer <[log in to unmask]> wrote:

>After upgrading from Windows 98 to XPpro on my Gateway desktop:
>shutting down sequence behaves normally and I can power on normally
>with the  tower on-off switch.  However, if I unplug the power cord from the
>wall outlet--the machine turns on all by itself  (without pushing the
>on-off switch) when the power cord is reinserted into the wall outlet.
>
>    In the power scheme I have unchecked "enable hibernation".
>
>                                Any thoughts?
>                                             Merrill (Ohio)
>
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