Steam --> Library --> right click the game (??) --> properties --> Local Files -->
1) Try verify the Integrity of the game (will take a bit of time depending on net speed and game size)
2) If the game still doesn't run after verifying the integrity of the game Just press the "Delete Local game Content" and after this complete right click the game and "install game"
try Option 1 First
Read his question clearly first then answer he already tried "verify the Integrity of the game cache".