Computer will not reboot after NIS 2011 installation

I installed Norton Internet Security 2011 on my Lenovo Z60M ThinkPad laptop running XP Professional.  During the installation it prompted me to unstall McAfee virus protection, which I accepted (and it completed)  I ran a ful computer scan.  I now have boot-up problems.  The boot.ini file disappeared giving me boot-up error "boot.ini file missing, booting from Windows" -- I replaced boot.ini from my latest backup and this message disappeared, but now have a very slow boot-up that frequently does not complete and sometimes will even give me the blue screen of death.  HELP!