I can only think of corrupted or infected files or a registry error... so
up
next should be to check for spyware, trojans or viruses... the MMC may be
actually hidden by such bugs. Go to C:\WINDOWS\System32\ and find the
file;
"MMC.exe"... if the file is there, (which is likely since you've run the
"sfc scannow") doble click on the file, and see if that makes the MMC
snap-in open or watch for any messages and make notes, you could also
check
the Event Viewer to se if any errors are registered. (Control
Panel\Management Tools\Computer Management\Event Viewer). Next check the
MMC.exe file for security permissions to your profile account, maybe take
ownership of the file and run several security applications and/or run
online antivirus & antispyware scans. Also go to
http://www.kellys-korner-xp.com/xp_tweaks.htm and download the registry
fix
from line 296 left, to lift restrictions to the Management Console
Sap-in.
If nothing helps, see if you can reinstall the Management Console from
Add-Remove programs in the Control Panel.
Recommended security applications:
Antispyware-antitrojans
A-squared free
Malwarebytes anti-Malware
Spyware Terminator
Super antispyware
Adaware 2008
For online scans, should you need to run any, type on the google search
engine: "online security scans", "online antivirus scans" & "online
antispyware/antitrojan scans"
Hope this helps.