First disable the network(If someone else is accesseing the same SEPM can create problem)....
Then run the resetpassword tool.. You have to wait for some time... then restart the SEPM service...
Then login... This will work for sure.....
How many SEPM do you have...
If you have replication setup... Login to remote server with old password and change the password...
Now replicated the servers... Once replication is finished you can login from primary server...