Minecraft launcher stuck on Preparing when launching forge

When I try launching any version of forge even if it's 1.8.9 or 1.12.2, it always hangs for no reason on Preparing!

 

Steps to reproduce:
1. Open Minecarft
2. Select 1.12.2 forge
3. Click PLAY
4. Launcher stuck on preparing, green button says "..." Please, help me!