Close Battle.net and all Blizzard processes via Task Manager.
This is the most reported and reliable solution. The core issue is likely that the language you have set in-game is not fully installed. starcraft 2 preparing game data link
Right-click and select Run as Administrator . Close Battle
Troubleshooting StarCraft II: Fix the "Preparing Game Data" Loop the bar gets stuck
), the bar gets stuck, or it happens every time you open the game, it becomes a major problem. Common Reasons for the Stuck Loading Loop