Mobo will not post

Disconnect all drives, both power and data cables.

Remove the RAM and re-install, making sure it snaps into place properly.

See if it boots. If not, remove all front case connections, except the power on/off and try again.

At this point, I would try building the basic components up outside of the case, to see if there's a short of the motherboard against the case. Pull the motherboard and the power supply from the case. Do not connect any drives but plug in the monitor.

You can power up the system by very carefully shorting the ON/OFF pins that run to the front switch after the power supply switch is turned on.

If this doesn't work, you need to carefully check the CPU to make sure you didn't install it incorrectly. If all is well there, then it's time to decide which components to return.

Basically, set it up like the system in this photo:

One thing, try a single RAM module at a time. If one of them is bad, this will isolate it.

If the system won't boot with either of the one modules, I'd guess it's the motherboard that is bad. But hard to prove without being able to swap out parts to test them. The thinking is that it's very unlikely that BOTH RAM modules are bad.

I'm assuming you removed everything from case and tried it as above.

If any of the 3 is no good, you'll get nothing.

CPU I would suspect only after motherboard. Assuming it's not damaged and installed correctly first time.