Kirk, I can open a new contact sheet window but the problem continues. When I closed PM (red button in Mac), I can´t re-open it. Sorry Kirk. I don`t know what you mean with all the menus disabled. I am a nwe mac user. Thanks again Kirk!
"I can't re-open it." What is 'it'? Photo Mechanic? Another Contact Sheet window?
In the "General" section of the Preferences dialog in PM, make sure you have the "On startup:" section set to "Open empty contact sheet" or any of the other choices besides "Do nothing".
In the "Contact Sheet" section of the Preferences dialog in PM, make sure you have the "Close contact sheet window when last tab is closed" unchecked, and set the "Create new Untitled window when resumed without any Contact Sheet window" checkbox to checked.
Were you a long time user of PM on Windows? I think what is happening is that on startup you have PM set to do nothing and when you close a window (you should generally close tabs and not windows) you see no window at all and think that PM is broken. While there is no preference to immediately create a new window when the last one is closed (that would be maddening for most users!), the above changes to your preferences mean that you generally should see a Contact Sheet window when you startup PM, or when you switch back to it from another application. Closing the tabs instead of the main Contact Sheet window should eliminate the last bit of confusion you're having.
Mac applications do not have a "frame window" like Windows apps. Mac applications have a main menu bar and document windows. Some Mac applications startup with a blank window, an open file dialog, or with no window at all and your cue is to look at the menu bar and begin by choosing commands from the menu bar.
HTH,
-Kirk