If you try to start the game and nothing happens, follow these steps:
Right click the PokeMMO launcher/shortcut and click "Open File Location".
Shift + Right click the folder background and click "Open Powershell Here".
Type .\jre\bin\java.exe -jar PokeMMO.exe and press enter.
If the game works normally after this step, you probably have set conflicting JAVA_OPTIONS. Please eliminate this variable, the following links explain how:
If the game still doesn't work, proceed to the next step.