Your brush tool is likly set to transparent. Look at the top of the screen in the options bar. As for your healing brush and selection edges - I suspect it's a graphics card issue. I've been having similar problems. To get the screen to refresh, I hold down the space bar and just move my screen slightly with the hand tool. The tools are working, you just can't see them.
If these suggestions don't fix your problems, please post a screenshot that includes the options bar and layers - so your whole screen.
Melissa Piccone | Adobe Certified Instructor | Adobe User Group Manager