I don’t know if it’s still around but the HP Partsurfer site would list all of the parts used for a model. You can also go to HP’s Warranty site, put in your serial number and there’ll be a list of parts used just for your specific computer from when it was sold. That’ll show the HP part numbers on it.

Try only putting 1 stick in in slot 1 and booting. If it works swap the other chip in and boot again. If both work then the chips are good and you can repeat with slot 2 and see if it works or not.

Could also check to make sure there’s no crud in the slot.

In the Display Settings click on the monitors that are showing up as a single monitor and in the drop down next to “Identify” change it to “Extend these displays”. I can’t recall exactly what it says when it’s combining them, might be “Duplicate these displays” or “Show only on”.