You are a little shy of information here.

What make of computer, what specs?

Did this happen before you installed SP2?

Did the shutdown freeze before you tweaked it? If not what did it do?

What happens? What error messages do you get? What else is displayed on the screen?

Have you contacted the manufacturer?

Have you tried Microsoft's Knowledge Base?

Have you tried a Google search?

Try this web site. It may help;

http://www.kellys-korner-xp.com/win_xp_restart.htm

Mark