Hello Ron,
I apologize for the inconvenience.
Will you try installing one more video driver for the onboard video?
Here is the Dell driver page for your PC. http://www.dell.com/support/home/us/en/04/product-support/product/optiplex-9020-desktop/drivers
Under the video tab, the second driver is for the Intel HD 4600 Graphics driver. Try installing this driver and then running the software with your monitor connected to the onboard video again.
Let me know if this changes anything.
Regards,
A.J.