Hello,
You can also try verifying the game cache, which makes sure that any missing files are downloaded and installed.
You can do this by going to your Steam Library, right-clicking Euro Truck Simulator 2 and then clicking Properties.
From the Properties menu, go to the 'Local Files' tab and then click 'Verify integrity of game cache'.
Once clicked, it may take several minutes to complete. Once it says all files have been validated, try running Euro Truck Simulator 2 again.
I hope this helps