How can I remove a folder without a name in Win7?

It probably has a name that you just can't see.

Try dir /x This displays the short names generated for non-8dot3 file names. The format is that of /N with the short name inserted before the long name. If no short name is present, blanks are displayed in its place.

More info type help dir or go here

Then when you have that name use the rmdir or rd command to delete the directory. (Or del if it's an invisible file)

I suggest you boot from a Linux Live CD (e.g. Ubuntu Live CD) and try deleting the folder.

After booting, go to Applications > Places and click on Home Folder to open Nautilus (i.e. the File Explorer for Ubuntu). Then check if the folder is visible and try to delete it with the right click menu.