Lightmass is not working with me any more. It was working fine a few months ago, but not now. It takes forever, or when finishing, it doesn't show up lightmass results, just crappy lighting.

I installed older versions of UDK and drivers, restore points, but... nothing, nada. I've tried everything is on my mind, with no luck.
My specs are: XP (32), ATI Radeon HD 2400

Any clue?