i have used space as iwt since the beginning with no problem at all
You should have no problem continuing to use Space for IWT, that's not what I'm saying.
What I am telling you is simply that you told me that you reset your WoW Key Bindings in the game... which means that -- when you do this -- IWT is not set to Space anymore in that window, it is set to nothing because it has no hotkey by default. Unless you configured it back to Space in that window, it's not going to work.
When you press Space in window 1, then -- as configured -- windows 2 3 and 4 should get Shift+Alt+N, then Left Shift+Backspace, then Space.Shift+Alt+N should make sure Click to Move is enabled, then Left Shift+Backspace should cause it to /assist the guy in window 1, then Space should cause it to Interact with Target. You can test each of those things in Window 4 right now.
Another thing you can do is look at the in-game debugging console to see what keys the game is receiving, and from where. Press Ctrl+Shift+Alt+G, click the debug tab, and tick the "Buttons" box. Then click "Show Debugging Console". Now when you send buttons to any window via Mapped Keys or broadcasting, it will tell you about it in this little box. So, press Space and then look at the debugging console in each window. It should show output matching the keys sent by your Mapped Key.
if nothing works, what should i do to start from scratch? delete and reinstall everything in a clean directory? or are there specific files that i could delete and recreate a character set with the same toons?
You don't actually have to delete anything. You can just go to File, Save As, and save your profile as something else. Then go to File, Clear. Then run the wizard again, and your ISBoxer configuration will be back in a known-good state.
But if you do this, it's still going to set up pretty much the same thing you have right now, minus a bunch of teams and a handful of custom Mapped Keys and Hotkeys. I am not sure this is going to solve the problem you are having.
Sometimes it's another addon causing a problem. For example some people don't realize that they made some Hotkey in Bartender that isn't listed. Then if I get them to do the Assist fix (which I linked you earlier and you said did not work) and they set something unbound to, say, Shift+Backspace or Ctrl+Shift+Backspace, then WoW will say what it was bound to. And then they say "oh... I looked through the list but didn't see anything configured to backspace but apparently my addon had something". So... just saying, the instructions tell you to do that for a reason.