I have not experienced the same problem, but I would suggest not leaving your legacy program open when you're not working at the computer. I would not leave any data entry window open either. Make sure to save your work and close Legacy if you're going to be away for a while. Otherwise you might risk a corruption of your data file.
If you still experience this problem, and depending on the age of your computer, you may want to consider a hard disk replacement. The disk may have issues causing you corruption problems.
I hope you can determine the cause of your issue so that you can keep it from 'eating' your data.
Good luck.
Brian