Have you tried: "Verify Integrity of Game Cache" or defragmenting cache files, etc? You could also try this Data Exception Prevention thing: https://support.steampowered.com/kb_article.php?ref=7169-TIAV-5361Just scroll down a bit and you'll find it.
Data Execution Prevention:1.Go to Start > Control Panel > System > Advanced > Performance > Data Execution Prevention. 2.Select "Turn on DEP for all programs and services except those I select:"3.Select "Add", navigate to C:\Program Files\Steam (or your default Steam directory), and add Steam.exe to the exception list.4.Additionally, you will need to add the executable (hl2.exe, for example) for any game you are seeing issues with. These files will either be in Steam\steamapps\common\<Game Title> or in \Steam\steamapps\<Your Steam Account Name>\<Game Title>\