Paint tools aren't working in Photopaint X6

Greetings!

For some baffling reason my paint tools have stopped working in Photopaint.  Even with all the layers flattened/combined; the transparency set to zero, feathering set to zero- I get nothing.  The line and fill tools work, and I can switch the paint and paper colors and use the eraser like a brush, but that's it.  It's getting a wee bit frustrating, and I'd appreciate any help any of you could offer.

I apologize if this problem has already been addressed here.  I looked, but could not find the solution.