Windows 2000 Professional problem

i have windows 2000 professional in my network ...1 week ago i found add/remove programs vanished...so i repaired my operatibg system with emergency disk...i found programon add/remove ,but i am facing other problem now..i.e i cant install any antivirus on my computer,even the stand alone nor the company anitvirus mcafee agent....and even when i try to install windows updates...it instals but i am unable to find windows updates on add/remove programs after windows restart...//can i know what might be the problem?