You might try running c:\windows\system\sfc.exe and
extract one file from installation disk. The file would
be RUNDLL32.EXE. You might also want to Scan for Altered Files to see if any others need fixing.
If your system was installed by professionals, the location of your "installation disk" is C:\WINDOWS\OPTIONS\CABS
If that doesn't work, you'll have to put the CD in.