Dell Latitude E6400 and E6500 series laptops periodically lock up and becomes unresponsive. If you can get Task Manager to load, it will show that it's CPU bound (100% CPU utilization) and that it's never the same application each time it lock's up.
The System Log in Event Viewer log will show:
Kernel-Processor-Power: The speed of processor 0 is being limited by system firmware. This processor has been in this reduced performance state for 71 seconds since the last report.
This is a known issue with Dell Latitude E6xxx series laptops while in their docking station.
According to Dell Technical Support:
This issue has been known and caused by the bottom plastics of the system.
Due to design differences, Dell engineering team have developed a solution to enhance ESD resistance to prevent this lockup from occurring.
You will need to contact Dell Technical Support to have the plastics on the bottom of the laptop replaced. Dell's Small and Medium Business Technical Support can be reached at 1-800-456-3355