The unit is a laptop model XPS 3780 --that is the model that was ordered and that is what was shipped.

Let's start with the system model.  Is this a desktop or a notebook?  And what's the correct model number (there is no XPS 3780, and the closest XPS is the 9380, which has no optical drive)?

The system model is on the label at the bottom of the system -- and on the setup screen.

XPS systems have not had optical drives in many, many years.  And even if it's an older system, there is no XPS 3780.  

To proceed, verify the model number.   However:

Since you're talking about a system that is the better part of a decade old, chances are the drive has failed and will need to be replaced.  Most times, these are standard drives --  but we need to know the correct system model number before we can render any advice.

None of the XPS 7xxx or 9xxx models built since about 2013 have had optical drives.

There is an Inspiron 3780 model -- 

https://www.dell.com/support/home/en-us/product-support/product/inspiron-17-3780-laptop/docs

If that's the model you have, the service manual is linked above.  First check to see whether system setup (F2 at powerup) recognizes the drive (look under Drives).  If it does not, the drive is dead and will need to be replaced.

Exactly - it's not an XPS.  It's an Inspiron 3780.  See above for the service manual and what to check.

If you need a replacement drive, try parts-people.com.

The laptop was purchased in Sept 2019

A screenshot of the Dell order is below