Check your brush mode in the Options bar.
What brush preset are you using? (Try resetting your brushes, and selecting the first brush in the panel.)
Are you trying to draw outside of an active selection?
What is your brush opacity set to? (It is oh so easy to hit a number key and set it to a very low opacity.)
Are your strokes hidden by a filled layer higher up the layer stack?
What are the layer blend modes set to?
If none of this helps, and you have not fixed it yourself (and I'm betting that you have) upload a screen grab showing your entire workspace, and make sure the Layers panel is showing. And please don't downsize before uploading.
I ended up having the mode set to something weird. thanks so much for you help though.
Thanks for letting us know. I do it all the time. Fingers move faster than my brain, and I action shortcuts I didn't even know were there! Or I just plain forget I was cleaning an alpha channel and left the brush in Overlay mode etc. etc. etc.