Some outdated mods are currently causing some players to be unable to launch the game, it will sit and not open. To resolve this temporarily while we work to fix the issue please unsubscribe from all Squad mods and then you should be able to re-install them on a case by case basis and figure out which ones are causing problems.
To do so go to the workshop and then "Your Files"
Then "Subscribed Items"
And then "Unsubscribe From All"
After unsubscribing please delete the following folder under your steam library:
workshop\content\393380
This will uninstall all mods from Squad.
If you continue to have issues please restart steam / your PC.