Manage My Computer Not Work

When I right click on MY COMPUTER and select MANAGE, it used to bring up things like the logs, services, and disk management. Now it just asks for file name that it can not locate the mmc.exe file. I pointed it to the system32 directory, but now allit says when I select MANAGE, it says MMC can not open file.
I tried reapplying SP3 but it did not help. I am the ADMIN of my machine.
This all started when people moved us to a new domain with new logins and stuff.
Any ideas because these gus are not helping.
Thanks.