PULSEMMC,

Thank you for using the Dell Community Forum.

Did you install any software or add any hardware prior to the system shutting down? Is there and error prior to shutting down?  On the back of the system are some diagnostic LED's. What is the pattern and color of these LED's? Try running the diagnostics on the system to see if anything comes back as failed. Dell Diagnostics Utility is a hardware 32-bit diagnostic program that is shipped on the Dimension Resource CD. It can be launched by booting to the Resource CD.