The / key works perfectly for the screenshot feature.
All we can guess is that you are doing something wrong at some point.
If your / key (not on the numpad, the other) is OK and your SDT version is OK, then you are unfortunately the only one with this problem... which is very likely to be some sort of stupid problem like "your key is stuck/dead" or something like that.
AFAIK, the screenshot x2 is an additional feature, you do not need to check it to take a "simple" screenshot.
As for the functionality, Faceless already told you that it opens a file dialog to save your screenshot.
Cheers