Contact Dell Support at 800.624.9896.  You will need to have the express service code and service tag available, which can be found on the workstation.  Explain what is going on to the Dell technician and you will be asked to perform a series of troubleshooting steps.  If this is a serviceable request, the technician will inform you of the next step to take whether it be an on-site visit, a shipped replacement, or what have you.  This Dell service will be of no charge provided the hardware is still under warranty and the warranty covers parts, labor, and an on-site option.

CU*Answers always warrants their Dell workstations for 3 year parts/labor/onsite with a Next Business Day (NBD) option.  The NBD option is determined on the availability of the part(s) being replaced.