It actually is illegal to remove the content lock. So use it at your own risk.
Important:
Some countries require content lock to be engaged: for example, Germany. If you live in a country where low violence settings are required, removing the content lock is illegal.
Anyways, there is a simple way to fix this, involving changing some registry settings
Exit from Steam, and open the "Start" menu in Windows.
Select "Run", type "regedit" and click "OK".
Navigate to the following registry key:
HKEY_CURRENT_USER\Software\Valve\Half-Life\Settings\
Right click the registry values "User Token 2" and "User Token 3" ,
choose "Delete", and then exit the registry.
Restart Steam.
Note: This fix only applies to the Half-Life games.
Best Answer
You can set the game to run in a borderless window through Steam:
Right-click the game in your library, go to 'Properties...', select 'Set Launch Options', type in
-windowed -noborder
, and click 'OK'. Twice.This should logically work for all Goldsource games.