A command symbol and period in place of your mouse cursor indicates that a script is running. On windows we see Esc as these are the keyboard short cuts for aborting a script that might be trapped in an infinite loop. Such a script could be set to start up automatically when you open the file or access a specific layout via script triggers or file options.
If this sounds like the situation you are dealing with, try holding down the command key and pressing the period to abort the script, then investigate to see what script might be running and fix the problem.
Please note that this keyboard controlled script abort can be disabled from within the script. If Command Period doesn't halt your script, you can open the script debugger and use it to halt your script if you have FileMaker Advanced.
Forcing open the file without having such a script start up can be tricky if you don't have Advanced, but it can be done. You can use Perform Script from a different file to perform a different "safe" script in the original file to cause it to open but without starting up the script.