My CS:GO gets stuck on 100 percent when its updating. When I click on the game to play it pops up the box that shows the estimated amount of wait time till I can play the game. The estimated amount of wait time shown is "0 seconds left." I have tried re-installing steam, but I still get the same issue. I have never had this issue with any other game before and this is the first time I've had this issue with CS:GO as I was able to play until I was prompted to update the game.
Just wait. Steam apparently doesn't understand that when people see "100%", they think their game is done.
When at 100%, Steam is still in the process of updating the game. Just keep waiting, don't close the window, and eventually it will be done, and you can play.