I think I may know what is happening in this case. If you open the problem notebook in a text editor, it doesn't contain any of the information in the original file. Instead, it seems to contain the instructions to display the welcome/exit page. I think that somehow, the contents of the welcome/exit page are being saved over the notebook contents. That is why when you open the notebook it appears that the welcome/exit page just stays put. Its actually opening the notebook correctly, but the notebook has been replaced with the welcome/exit page. Tough luck.

I would recommend saving through the file menu in the future, and never just clicking the close button (X) to save.

The next step would be sending the notebook, an explanation of the behavior, and what you tried to support@wolfram.com.

It doesn't seem to work, for me at least. In the beginning I also had this problem. And it was very frustrating to see that happening. I have disabled the closing window... and the problem persisted, but in another form:

Let's say you have a new notebook containing some code. Without saving the work, close the notebook by pressing "X"; it asks if you want to save your work; indicate the location and save. Now, if you want to open this recent notebook, first try and find it!

Try this to open the problem notebook:

File menu - Open
Locate the file and click ONCE to select it
Click the Options button low in the file navigator window
In the window that opens, check "Parse and Load Entire Notebook .."
Close the second window
Click OPEN in the file locator window.

See the screen shot.

This will rebuild some internal information that might be keeping the notebook inert.

I've got the same problem. I got mathematica 10 for work, and I have two files. One opens without any trouble, with the other one it is the same issue as described above. (The file contains possibly unsafe dynamic content) Clicking on x or on "enable dynamics" does not seem to do a thing. Both files just contain some simple calculations and no actual programming (but rather a lot of those, so recreating them would waste several hours...), therefore I can't imagine why the problem occurs. But maybe this is just because I'm new to mathematica. Anyway, help is much appreciated because I can't do a thing right now :(

The window in your screen-shot is the exit screen. I'm not sure why that is appearing. Do the three buttons below it ("New Notebook", "Open...", "Quit") work?

If you haven't tried this yet, please follow the instructions in this article:

http://support.wolfram.com/kb/12464

Is Mathematica opening normally otherwise? Are you able to run it, create a new notebook, type in it, save it, restart Mathematica, and then reopen the file?

What operating system are you using? When say that nothing happens after you click "Enable Dynamics", do you mean that the notebook doesn't appear on the screen anymore?