Bare with me, the following is a bit winded.

I have Ubuntu 10.10 Desktop 64-bit installed on my laptop and up until a few weeks ago it has been running great. Then one day, while I was not using the laptop it froze. I was logged in as my user but had locked the screen locked and closed the lid. I didn't notice that it had frozen until I opened the lid and wiggled the mouse to try and log in. The screen remained black and I got no response. I immediately tried Alt + F2, F3, F4, etc. but got no response. The only thing I could do was hold the power button to power off the machine.

The freezing has happened as quickly as within 10-20 minutes of the system being logged off and lid closed and as long as 4-6 hours. My machine is NOT configured to go into standby when plugged in and this has happened both on AC power and battery.

Troubleshooting I have performed:

I uninstalled programs I knew that I had installed between when it was working fine and having problems. Those programs were CrashPlan, Shutter and Conky. After uninstalling ALL of these programs the freezing still occurs.

Next, I decided to SSH into the machine from my desktop and leave an htop and tail of the syslog running. Here are screenshots of the last thing shown on both when the system froze: htop, syslog

Here is a dump of my syslog after another freeze. The freeze happened at 9:14 and I didn't notice it until about 10 minutes later and rebooted, hence the 10 minute gap from 9:14 to 9:24.

In the above syslog dump I noticed a lot of NVRM: os_raise_smp_barrier(), invalid context! and upon investigating that message learned it was from the proprietary Nvidia driver I had installed. Thinking this could be part of the problem I uninstalled the Nvidia driver and reverted to using the Nouveau driver. The computer still froze after a few hours.

Lastly, thinking the problem could be caused by overheating I used compressed air to blow out any dust in the CPU vents and all other openings on the laptop.

None of the above troubleshooting has helped and the freezing still occurs. What other steps can I take to troubleshoot and/or fix this problem?

Note: Yesterday X started to eat up a lot of CPU power and eventually froze my system while I was forwarding an X session over SSH (from another PC to my laptop). I'm unsure if this is related or not as it doesn't match any of the symptoms of the problem above. Aside from this, the system has never frozen while in use, even under heavy load.

EDIT: I just ran Memtest86+ and it made it through two passes without any errors. Just eliminating possible causes here.