Hi @dell580 ,
What BIOS version is currently installed?
According to the Dell support page for your model, the latest BIOS version is A07 which was released in 2012.
If you already have this version installed and are getting an error message it may be a conflict between the OS and the BIOS.
Dell does not offer driver support for Win 10 for your model. It only offers driver support for Win Vista and Win 7
Has the HDMI port ever worked in your computer with Win 10 Pro?
If it has worked before in Win 10 Pro, then perhaps a Win 10 update is the cause of it not working now. See if you can recall when the problem first started and then check in Settings > Update and Security > Windows Update > view Update History and see if there was an update about the same time that the problem started. If so, uninstall the update (click on uninstall updates and select the required update) follow the prompts and then restart the computer and check if it has resolved the problem.
If it has resolved the problem then the only problem now is that Windows will reinstall the update again the next time it looks for updates. You are fortunate that you have Win 10 Pro because you can prevent updates from occurring so you have a little more choice. The downside to this is that your computer may be less secure in the future unless you manually update. Here’s a link that explains it better than I can.
If has never worked in Win 10 Pro then perhaps it is a compatibility problem between Win 10 and the BIOS.
You could always check the display adaptor manufacturer’s website (check in Device Manager for make and model of display adaptor) to see if they have Win 10 drivers available for that exact model display adaptor and see if that works. There is no guarantee that this will work as computer manufacturers sometimes modify the display adaptor and the drivers to suit their particular motherboard requirements, but it is worth a try.