LR 8.0 worked well at the start, several weeks ago. But now it is not! When using adjustment brush to edit an image the screen sometimes goes black and at top "not responding". Also has become very slow when using the adjustment brush. Updated graphics card driver, but same whether checked or unchecked in LR. Talked with Adobe support and they had me optimize catalog only. Still the same. Today I uninstalled then reinstalled LR no change. It is at a point where it takes way too much time to now use. Need help!