Can't Find Windows Installer in XP

[Sandy]

I tried to reinstall a program I had recently removed via Add/Remove
Programs. I got this error" The Windows Installer Service could not be
accessed. This can occur if you are running Windows in safe mode, or if the
Windows Installer is not correctly installed." I followed Microsoft's
advice to check the registry for the path to MSIServer. I cannot find it in
the registry. I also checked for Windows Installer in Administrative
Tools/Services to see if it was disabled, but it is not listed. Has anyone
else encountered this problem in Windows XP? Thanks for any assistance.
Sandy