Firewalls or antivirus programs sometimes modify or block the file. How to Download and Install Masterservers.vdf
If you still see a blank screen after replacing the file, try these secondary fixes: Check Your Firewall Rules
To get the full, working MasterServers.vdf for Counter-Strike: Source , follow these steps:
This file (located in platform/config or similar) tells the game which master servers to query for a server list. Modifying it can redirect your game to unofficial server browsers.