Check your dir structure, should be ...
C:\Program Files\Stardock\Sins of a Solar Empire\ParticleForge.exe
not
C:\Program Files\Stardock\Sins of a Solar Empire\ParticleForge 3\ParticleForge.exe
not sure if thats the problem but its common while extracting
Again From that link
Installation
After downloading and unzipping the tool from the Sins website, make sure to copy the contents of the Particle Forge folder (minus the PipelineEffects) into the game's root \Program Files\Sins of a Solar Empire\ directory. This must be done so that Particle Forge has direct access to the Mesh, Textures, and TextureAnimations folders. Otherwise, the program will not load the textures automatically, and the preview window will unhelpfully show every particle as a solid square.
That means all the files to your root accept the folder PipelineEffects