Were you hacked after you played CS:GO? If that is the case i know what happend.
You joined a server. Which had a keylogger (Right now coumminty servers are not 100 % safe) After you closed your game a browser came up for like 5 minutes or so. And then it crashed all your shit. And you need to restart. After in this case he took your account instead of taking only the skins and leaving. And as you couldnt open the browser. He might have access to your email, connected to your steam account, Remove the steam guard email. And its all his.
NOTE: For all those who plays CS:GO in coumminty servers. There is rumors that MOTD can get you vac-banned so i suggest to do this cl_disablemotd 1If it dosnet work ill come up with the real code