When using Target Manager, make sure that everything is prepared before you try to connect and attach. Make sure that when you turn on your ps3, Target Manager is able to Connect to your console without any problems. From there, you want to DOUBLE CHECK your EBOOT to make sure that it's a working one. And if so, you want to navigate to your preferred game, and begin the Connect and Attach process.
If this still doesn't work for you, then your best bet would be to install Control Console and use that. Hopefully, you figure out the issue in a timely manner.