Reseat the ram again. Sometimes you need to put a little bit of muscle to get the ram into desktop mobos ram slots. Assuming this is for your ASUS TUF PLUS-GAMING B450M and not some laptop.
If that doesn't work, try just one stick at a time to narrow down if 1 stick is causing a problem as a static discharge could have killed one.
If that doesn't work...make sure your monitor is plugged in.