I insert my Radeon RX 560 (4 GB) graphics card into my HP Envy 700-074 and get a black screen. No display. I am running Windows 10. If I remove the card, I can go back to mobo driver. So, (1) Will this card work on this machine? and (2) If it will, what do I need to do to make it work?
It likely will work (given correct settings and other hardware).
You have not given much information so some random ideas on what could be the issue.
It could be a bios issue such as having it initialize the PCIe slot with the new card first this is usually the PEG option.
It could be your bios needs to be updated.
It could be your power supply doesn't meet the requirements for the card.
It could be the card wasn't all the way inserted.
I would check those things first. If none of that helps or you happen to have another pc handy try the card in another machine and see if it posts there.
Check your BIOS for Legacy Bios or UEFI BIOS (If your graphics card is older than a few years and was not originally for Win8/10 this may be the issue if set to UEFI). If you are in Legacy BIOS it should work, if in UEFI try disabling Fast Boot.