CS4 Tools Intermitantly Stop Working ! Fix?

[littlecynicism]

The brush, eraser, clone tool, dodge/burn, etc. randomly stop working while I'm on a project. Then, just as randomly, they start working - five, ten, twenty minutes later. They can be resized or modified in other ways during this time. I can still use the pen tool, make selections and apply gradients.

I have tried closing down Photoshop and holding down crtl>alt>shift while restarting and then the tools work for several minutes before the same issues ensued.

I reset the tool preferences as well, that does nothing.

I called Adobe tech support, but without the seriel number they are beyond worthless (my family owns the thing, they just can't remember what they did with the seriel number!).

Anyone else had this problem? Anyone else no how to fix it?