Computer never shuts down, just restarts

ok i have a very annoying problem with my computer that just recently started happening. ive noticed that it started happening after i installed windows service pack2. that could be the reason and maybe not. anyways every time when i got to the start menu to shut down my computer it goes thru the shutting down process like normal but when it shuts down my computer never turns off. instead it just restarts and starts loading up windows again. the only way to turn off my computer is wait for it to shut down then hold in my power switch for the some amount of seconds i need to. the same exact thing happens when i tap the power button. it logs off of windows and shuts down but never turns off. it just restarts and loads right into windows. has anyone ever had this happen before, or does anyone know what im talking about?

ACPI is responsible for shutting down your PC the "new" way, so make sure ACPI is enabled in the BIOS. If in doubt, reset the BIOS to its defaults if you know what you are doing.

Updating the BIOS of your mainboard may also help.

SHUTDOWN & RESTART TROUBLESHOOTING
http://aumha.org/win5/a/shtdwnxp.php

I have the same problem with my system, so you aren't alone. It worked fine for a very, very long time. Then one day, for no memorable reason, it only restarts even when shut down.

I really haven't had the oppotunity (or the will) to figure it out. Shame on me!

But if I find an answer for it, I'll be sure it post it.

SHUTDOWN & RESTART TROUBLESHOOTING
http://aumha.org/win5/a/shtdwnxp.php

thank you very much, that fixed the problem.