Hi DBHinRB,
Try to perform BIOS default. Restart the computer and tap F2 on Dell logo and hit F9 to Load defaults. Now save and Exit BIOS.
Check if the computer boots now.
Also, refer the below link for Hard drive and CD/DVD drive troubleshooting:
If the issue persists, swap the hard drive and DVD drive cable on the motherboard.
From the above link click Manual and Documentation and Service manual to access hard drive and DVD drive reseat/remove section.
** NOTE: Please ensure that the power cable of the computer is disconnected before opening the chassis. Refer to the Service Manual for assistance on removing or replacing the internal components of the computer.
Note: Reseat or replace the hard drive/ DVD drive if you are compfortable in doing so.
Awaiting your response!