Deletion of page within Website Master held on PC

I may be doing something completely wrong but my Host requires the website start page to be 'default.html' which is OK. Uploading is fine but then when I go back to Dreamweaver8 and look at my web pages I find that 'default.html' is now blank with the exception of the following 3 lines of code:

<?xml version="1.0"?>

All of my original code has gone. Can someone explain why or better still a solution please.