I'm still having this problem, so I took my PC into work to have time to look at it and found nothing wrong. There is no pattern to the lockups, but there is a pattern of behaviour prior to and during the lockup. 1. This always happens when running a Mozilla browser on websites both with and without Flash content. Browsers it has done it with: Firefox 3.6, Firefox 4, Pale Moon 3.6, Pale Moon 4. 2. When the computer "locks up" it is actually running. If I wait a couple minutes from doing a hard reset or shutdown, EventLog will log the correct time of shutdown, not the time of supposed lockup. 3. The keyboard stops working first, even if I am not using the keyboard. The mouse cursor will still move around but will eventually stop. 4. The HDD activity light will be active (not solid, not off) during the time of lockup. (NOTE: I haven't waited to see if it unfreezes) 5. By checking event logs, there is a pattern in the SYSTEM log that appears EVERY TIME this happens. Here is an example. EventLog (from after reboot): The previous system shutdown at 9:36:47 PM on 4/5/2011 was unexpected 4/5/2011@9:36:23 Windows Error Reporting Service entered the running state 4/5/2011@9:36:00 Multimedia Class Scheduler service entered the running state Now every lockup I have experience show the WER and MCS services starting less than a minute before the reported shutdown time. Of the 7 times my system has locked up, this has been constant each time. Not sure what that means.