I am on WINDOWS 10. 64gigs of ram. I bought ACID PRO 10. Included was Melodyne. Worked the first time I started it in acid, where it was viewable through vendors/Celemony. Went to use to use it tonight. It was nowhere to be found. Went to the Melodyne stand alone program. Got tricked into purchasing a second seat since the website said it was operating as a trial with no simple way to put the serial number in, but whatever. It's now properly registered and I now own two seats on it. No biggie. Went and made sure it was installed properly. Found the .dll for it in the programfiles/common folder, copied it into the VST3 folder as well. Went back to ACID and its still not showing up in the file tree. Vendors/Celemony. The folder is there, but the plugin is not within it. Why is Acid not recognizing it and allowing me to use it? (Version 10.0.4 build 29)

You are not alone, I have yet to use mine. Its grayed from day one.

Going off topic but may help save you a headache: I gave up on it and actually avoid anything Magix added other than 64 bit to AP line. The more you stay away from the new "features", the less the program will crash. Mine finally started working without crashing, just as long as I don't touch an MP3 file, Morph Pads, Magix VSTs and Effects and stick with 3rd party plugins, its a happy life and i am enjoying making music in AP10.

So, you might want to use Melodyne as standalone if its possible. I own Studio version of Melodyne so just use it standalone and things are fine. I have accepted the fact that I paid a lot of money to use Acid Pro once again in my life and ignoring the extra features it came with.