I'm not quite sure I understand.
You had mysql installed via apt-get.
Then you installed another binary package on top of that?
If yes, what kind of binary package?
You will have to clean it up completely and then reinstall. Otherwise you risk having files from the wrong distribution around.
If you have installed the second package from a simple tar archive (a .tar.gz or a .tgz file), then you can use
tar tvfz FILE
to get a list of the files installed. You will have to remove those files by hand, just as you installed them by hand.
Once you have cleared out the second manual install, flush the debian install with
dpkg -P mysql-server
At that point you should be able to start from scratch and reinstall mysql, webmin etc.
If you stick with debian's packages, you'll get installations of mysql and webmin that work together.
As for starting and restarting, in Debian you use
to control it.
I hope this helps you a bit.