when i shut down my PC it always restarts its self in is xp home edition software

Do you have SP2 & all subsequent updates?

Do you run virus & spyware scans?

See if anything here helps:

http://aumha.org/win5/a/shtdwnxp.htm

yes sp 2 and updates installed

and running virus and spyware

Did you read this:

http://aumha.org/win5/a/shtdwnxp.htm