had this problem. An new to Indesign Pen tool...after all these years of avoiding it, and was drawing simple map for driving directions. Then it would not work AT ALL...for new lines. I could however select and continue to work on the existing line... modify it. But could not add to it outside the existing line.
Pressing P got it to work again...quick test and drew a rough shape.. Whew. Yep Now I can complete the shape...filled it with color. Whew.
I was ready to reload the program. Toggling P does not seem to DE activate the Pen tool. Any idea how this got deactivated in the first place?? Being up near the - = keys imagined I hit P by mistake, but ???