Nowhere legal. Siemens does not offer a free trial for ST4. Use Fusion 360 or FreeCAD for zero-cost alternatives, or buy a used perpetual license from a reseller (prices range $500–$1500).
Fix: Close any background apps (OneDrive, Dropbox). Restart Windows Installer service (run net stop msiserver then net start msiserver as admin).
If text is blurry:
ST4 uses up to 4 cores for regeneration. Ensure in Options → Assemblies → “Use multiple processors” is checked.