Hello Teja,
If I understand correctly, you cannot administer (stop, start, etc) a certain SAP System from MMC because you forgot the password.
You should be able log in with the <SID>adm user account which was specified during the installation.
And depending on the configuration selected during the installation it is possible that an OS admin user is also able to start the system.
If nothing works you can use the emergency user protocol to get into the system again.
Best Regards,
Peter Tari