In Win 7, when copying a file "ABC.def" into a folder that already contains a file with the same name, the new file is copied with a "(2)" next to the name. Like this: "ABC (2).def" No popup to select whether to replace or leave both files is displayed. I want to know where is the setting to prevent keeping both files.
Are you using Teracopy or any other shell extensions that manage/take over file operations?
If you are, I would look in the settings of that application, however if you are using Explorer / normal drag and drop or similar, this is not normal behaviour, and I am not sure what is going on.
You should be seeing something like this:
If you are not then, please reply with the steps you use to copy the file.