Starting a week or so ago, I tried to log on and everything seemed fine until about three seconds after the loading progress bar vanished. My character appeared and the landscape started to fill in. I started moving -- and then everything stopped. The program would no longer respond at all and had to be force-killed. I tried SL just now with the latest update and the same thing happened. I thought the problem might be that it was crashing when I tried to turn, but this time I just ran the program and waited a few seconds.
My computer used to run SL and hasn't undergone any major chances since then.