Same problem here, started running the game in window boarderless mode to avoid black screen / crashes forcing me to power cycle my machine.
to do the same, right click on Source SDK Base 2007, choose properties, choose launch options and put
-game "D:\Steam\steamapps\sourcemods\gesource" -windowed -noborder -w 2560 -h 1440
change \steam\steamapps\sourcemods\gesource to your steam dir, and change -w and -h to your screen resolution
so for default steam install and 1920x1080 =
-game "C:\Program Files(x86)\Steam\steamapps\sourcemods\gesource" -windowed -noborder -w 1920 -h 1080