New build Ryzen 1700, no display/boot screen

Start over, take the board out, and see that you don't have any standoffs in the wrong spot, that will shortout your board.  Ask me how I know.  :(  Killed a board like this once a while back.

If you're good there, then double check that you seated the CPU properly, and that it isn't raised up, and you bent the pins.

Check.

Then as you have done before use a single stick of RAM in the A2 spot, but I don't think it matters for a single stick, which slot you use.

Double check that your CMOS reset jumper is in the right spot, and that the CMOS battery is also sitting flush, and has not popped out.

Double check all 12v power cables are fully inserted into their slots on the motherboard from the power supply.

Take out your videocard, and see that there aren't any obstructions in the PCI slot, use some compressed air if you have to.

Not sure what kind of case you have, but check for any spots that might cause a short, metal on metal.

Try another PCI slot for your videocard, just to get it to post.

Actually, try everything outside of the case, on top of your motherboard box first.

Could be a bad piece of hardware, it happens.

If you're reusing an SSD, storage drives, try a single drive, or try posting without any drives connected at first.  I've experienced systems not posting due to a bad drive.

That's it from me, good luck.

Edit:  Big no no, that I recently discovered while building my Ryzen system was using power cables from different modular power supplies of differing brands.  DO NOT MIX!!!  The plug might fit, but the pins might be different, and you can damage and break hardware that way.  I got lucky, my eVGA PSU had protection built in, so it wouldn't allow the system to power up past a quick blip.  I was using extra cables that were longer from a Corsair power supply I had.  Yeah, stupid I know, but they don't tell you not to mix power cables anywhere, and usually if it fits, it sits with computer cables.