1-Salte de steam presiona la tecla de windows luego busca steam click derecho y abrir como administrador
2-Abre tu Cmd como administrador para abrirlo presiona la tecla de windows y busca cmd click derecho abrir como administrador luego pega lo siguiente:
"C:\Program Files (x86)\Steam\bin\SteamService.exe" /repair
3-Ve a steam biblioteca luego csgo click derecho propiedades beta y selecciona alguna beta luego que se te alla descargado cambia la beta que pusiste a salir de las betas

1.- Close Steam, press the windows key then search Steam: do a right click on Steam and open it as Administrator

2.- Open your CMD as administrator; if you haven't idea how to do it, just press the Window's key again and search CMD, click it with a right click and open it as a administrator, after that just copy and paste that text:
"C:\Program Files (x86)\Steam\bin\SteamService.exe" /repair

3.- Go to Steam Library, do a right click on CSGO, click on Properties then go to BETAS (it's in the top, behind the LANGUAGE) and select whatever beta, when you downloaded it go back to betas and you'll select the option "NONE - Opt out all beta progams and that's it