I've tweaked a few HP towers in my day. Luckily none in the past couple of years. They tried way too hard to make proprietary components like Dell does these days. Not sure if that continues to this day, but things like taking a STANDARD USB header plug, inserting an extra row of blank, unused pins, so that no other *standard* plugs will work with their motherboards. Well.. a dremel and a cutting disc later, I got it working.
Regardless, I strongly suggest if anybody is at the point they are able to reliably swap out a CPU, change ram sticks, plug in a graphics card (all pretty basic stuff): Build Your Own! Put your own basic tower together and avoid all those proprietary attempts to rule the word that HP, Dell, and the like, are engaged in.
Just get a fresh motherboard with a standard BIOS, and standard connector plugs. You'll be happier in the long run and will be able to better upgrade in the future with less stress and less hassle.