My guess is that your operating system got updated to Mavericks and that you are running an old version of Lightroom:
Sliders are white, look different | Mac OS X 10.9 Mavericks
Be aware of a Lightroom bug with color management in mavericks that makes shadows too deep in the Develop module: Jao's photo blog: Serious color management bug in Mac OS 10.9 "Mavericks" and Jao's photo blog: Further quantification of the Mavericks color management problem.