Recently, I experienced a lot of hard lockups on my desktop computer running Ubuntu 8.04. When lock up occurred, everything just halted. I couldn’t ssh to it to restart, everything just stops. Only hard reset would help. Computer specs are: MB Gigabyte P35-DS3R, Core2Duo 2.33Ghz, 2GB RAM, NVidia 7900GS…

What was the problem? NVidia drivers. And speedstep/powernowd. When computer was in idle state, processor worked at 2.0GHz, under the load it worked at 2.33GHz. Sometimes when frequency changed, computer crashed due to NVidia drivers.

Here’s the solution:
Disable powernowd. Quick and dirty fix is to edit:

/etc/init.d/powernowd

After #! /bin/sh in new line add exit 0 so it looks like:

#! /bin/sh
exit 0
# Init script for powernowd
#
### BEGIN INIT INFO
...