Sandbox isn't working

My single player sandbox game-mode freezes mid download than takes me back to the main page, I have tried…

  1. Deleting all my adding
  2. Reinstalling garrysmod
  3. Playing multiplayer (works fine)

Help please

Just to confirm, you did buy this on Steam right? Pirated versions will have problems that cannot be fixed. Also try validating the game cache as explained here https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335

This is why it’s happening:

Uninstall your game, delete the garrysmod/garrysmod folder and reinstall

it also happened to me today, was not happening to me earlier I didn’t install any new addons yet but ill see what causes it