There may be other factors causing your games to lock up - please review the Using a Firewall with Steam topic and the Programs which interfere with Steam topic to ensure a firewall or background applications are not interfering with Steam.
If you see purple checkerboards, missing weapon models, or missing world models, especially in Valve titles, please review the Verify GCF Cache Files topic for troubleshooting instructions.
The following steps may help troubleshoot video and/or display issues in most games:
See the Updating Drivers topic for instructions to ensure your system is using the appropriate/ drivers for your current video card.
Check DirectX settings and update DirectX to improve graphics display quality.
Note: The following process is only compatible with Valve titles. The commands will not have any effect on third party titles.
See the Reset Video Settings and Force a Video Mode topic for instructions to use autoconfig and experiment with resolution and refresh settings - it is recommended that you start with the lowest resolution your video card and monitor will support, then work your way up until you find a video mode which displays correctly without straining your system's resources.
While the following video cards are listed as having DirectX 7.0 hardware support, (the minimum requirement for running Source-engine games) they are not supported:
Please see the Left 4 Dead Video Errors article.