Black Screen

After the last update (not todays) I started getting a black screen 10 mins after logging into SL and would have to manually shut down and restart. I would do this twice and then the rest of the day I would be fine.

With TODAYS update I can't go in for 30 seconds without getting black screen, comp freezes and I have to manually restart. I can't do anything but push that button and hold it until my comp shuts down. This is extremely frustrating and I'm not sure if its the same issues as the crashing or if its a whole different issue.

I have a Radeon 9800 PRO video card and the lastest drivers installed. Please help