Issues Still With Import Backup dat.file
From Microsoft's documentation on how to open a command prompt window:


  Open the Command Prompt window by clicking the Start button, clicking All Programs, clicking Accessories, and
  then clicking Command Prompt.


Also:


  Here's another way to open a Command Prompt window: Click the Start
  button. In the Search box, type Command
  Prompt, and then, in the list of results, double-click Command Prompt.


Once you do that use the cd command to "change directory" to wherever Bitcoin is installed to (probably C:\Program Files (x86)\Bitcoin or C:\Program Files\Bitcoin).  From there you should be able to type bitcoin-qt.exe -rescan and be on your way!