Hi... I'm dying. Two days without editing!!
I click on the adjustment brush and it will let me adjust the size of the brush, and I go to "brush" and nothing changes. I switch the saturation, brightness, contrast, etc, and NOTHING happens; however, it does record in the history with what I've done ("Add Brush Stroke", "Update Saturation Adjustment", "Update Brightness Adjustment", ect.), but I see no visual evidence. @ the same time, ALL of the other tools work fine. I can also change the saturation, brightness, etc. of the entire picture, just not using the adjustment brush (which is my FAVORITE tool) in the spots I need. I've been using it for months now with no problems... and it just stopped.
I tried the advise you gave Helen about pushing the H and O, but got nothing. I've uninstalled every remnant of lightroom and reinstalled, updated, etc. and nothing. Please help!