Go to the Library in Steam,
right click Portal 2>Properties>Local Files>Verify Integrity of game cache,
then wait for it to finish and try to launch the game again.
You need to buy Portal in order to play the mod Portal: Prelude.
You can still play the game if you go to EA > The Sims 3 > Game > Bin > TSR.exe but I'm not sure how to actually fix the launcher. Sorry.
I know I get that to whenever I go on to the launcher I click on the play button and it goes white and it takes ages to load...I NEED AN ANSWER
I don't think there's a difference between professional difficulty and other difficulties. You just have to buy the RPG-7 with 30,000 pesetas or for the infinite Rocket Launcher, you have to play another round (load round) after you finished one round.
go onto map maker and load the map you want to play on then press export next to the save and test button wait for it to export then go to cape of distant worlds and look for a portal about half way down and the name of your map will be above the portal
you can play mario bros with portal gun online
kaijudo portal kaijudo portal
In order to play the mod Portal: Prelude, you do need to have Portal.
darude - sandstorm
You play as Chell the same as in the first portal and In CO-OP, you can play as two robots named Atlas and P-body
Urm... you just buy Portal 2 from Steam and then play it...
You go to a website called technic.net and you then download the technic launcher. After that you can open the launcher, select tekkit, login and play.