I just replaced my 2x4GB 2400MHz Corsair RAM with 2x8GB sticks of 3200MHz HyperX RAM. The RAM looks like it's in fine, and my PC turns on, but my (MSI) monitor says it has no signal. I've triple-checked that all the correct things are plugged in, so I don't know why it doesn't work. Also now, my old RAM doesn't work.
I'm a noob, so I might be missing something obvious.