device driver 270.28 unstable in Windows 7? both laptop and desktop drivers

I installed the latest driver from CUDA 4.0 on two Windows 7 computers.

  1. One Toshiba Qosmio X505-880 laptop with GTS 360M: has been unstable since I installed 270.28 driver. Problems: whenever the screen displayed is turned off for whatever reason (log off, change font size, hibernation, etc), it remains a black screen and will not wake up. It leads to a blue screen once also. I can do nothing but restarting the computer to restore the display. Windows 7 works fine with my early driver coming with CUDA 3.1.
  2. One workstation with one Tesla C2050 and one GTX 580: similar symptoms as the laptop. I don’t use it very often. It actually becomes frozen after some time. Black or frozen screen. No response to anything. I have no choice but to restart the computer. After restarting, it will become frozen again after a few hours. I did not run anything after it starts up.

Any fixes? Thank you,