Hi Everyone!!! Boot up Problem...........sp2

Well, my situation is i have windows xp 2000, i reinstalled it and downloaded the sp2. Ever since i downloaded sp2 i have been having trouble with my boot up. Not sure what happened, since i have never had a problem with downloading sp2 before. Is it possible to reinstall windows xp 2000 without installing sp2?? Im using Zone Alarm Security Suite 7.4 for a firewall, and was also wandering if it would affect my zone if im not using the sp2. I could surely use some insight on this since i dont know much about computers. Any information is greatly appreciated.