I have been trying to troubleshoot this laptop for a couple of days now.
It has hung about 8 times in the last two days. It will become completely unresponsive except for CAD. CAD will show the appropriate screen but if you try and Log Off/Shut Down/Task Manager it freezes again. After being in the frozen state for an indeterminate period of time it will often start a continuous beep, which can only be stopped by a hard power off.
The interesting thing is that it seems to run into the problem when you are not using it. When you return and try and use it the mouse will move slightly and then will hang.
I was convinced the problem was related to Windows Desktop Search as I was getting errors relating to that, however, I uninstalled it and no change. Now I am starting to suspect IE8. There is really nothing much installed on this PC, Office 2007, Roxio crapware from Dell, PowerDVD, AVG, ATI Catalyst Control Center, Autocad 2004.
It is completely patched from Microsoft and from Dell. It has an up to date anti-virus that is indicating no problems. I am getting no entries in the event logs indicating a problem.