My Windows 7 Pro 64bit PC crashed with a BSOD (MEMORY_MANAGEMENT) while working in LR 4.2RC and now most of the sliders in the Develop module do not respond to click and dragging. Certain sliders still work: Basic - Tint, Tone Curve - none, HSL - All, Color - All, B&W - none, Detail - none, Lens Correction - none, Effects and Calibration - both none. I can click on a point on the slider bar and the slider will be moved to the position. Can double-click on a bar and it will be reset. Just cannot slide most of the sliders.
Very strange. This is not a PC that crashes a lot, kind of suspect LR for the BSOD.
I have not had any crashes at all (using LR4 RC2 or any other program...never a Blue Screen of Death) on my Windows 7 Pro 64bit pc. You say that your PC does not crash a lot....so it has crashed some? If it does crash while using other programs, I would suspect that it is not caused by Lightroom. I wish I had an idea to help you, but I do not. Good luck.