Is this a new problem? Were things working OK previously? Any new hardware or software?
If this is a new problem try a System Restore to a point prior to the problem:
start > All Programs > Accessories > System Tools > System Restore
If there's a large blank space in the list, read this (courtesy of Kelly Theriot MVP):
Add or Remove - White Space
http://www.kellys-korner-xp.com/xp_a.htm#ws
If the list is completely empty, try these suggestions from a KB article:
Add/Remove Programs tool displays installed programs incorrectly
http://support.microsoft.com/kb/266668/en-us
