Quick and Easy:
1. Click on the 
blue circle in the upper left corner of Legacy. You might have customized Legacy to have a system menu instead of the blue circle. If this is the case please click the word system at the top left instead of the blue circle.
2. In the list of Recent Family Files, select your file.
If above quick and easy method doesn't work, you can have Legacy look for the missing family file:
1. Start Legacy and click on File and select Open File.
2. The Open File dialog box will open. Click on Have Legacy create a list of files to choose from. Legacy will collect and display a list of all the appropriate files from all the drives on your computer. This is recommended if you don't know where or how to find your family file. If you have set Legacy to not show the open file dialog box then you may need to set your options to turn this back on. To do this go back to the main Legacy screen and go to options>customize>12.5 Message Boxes and click "Turn on or off optional reminder messages". In the following pop up in the messages tab at the bottom set it to "give me a choice of how to select the file". Now you should be able to create a list of all files on your computer following these instructions.
3. Highlight your family file and click the Select button to open your family file. (You should click the Refresh List button if you have deleted, moved or renamed family files since the last time you used this list, or just don't remember.)
4. If Legacy cannot find your family file, restore it from your backup copy. Please see the article "How to Restore a Legacy Family File from a Backup Copy in Legacy" at http://support.legacyfamilytree.com/article/AA-00869.
5. Once you have your file back, you can set it to open whenever Legacy is started. Please see the article "How do I set Legacy to always start with my preferred family file?" at http://legacyfamilytree.host4kb.com/article/AA-00835.
