Minecraft – Screen flickering in Minecraft

Roll your drivers back to your previous version and see if the problem still persists. If so, it might be a recent patch for L4D2 that made it incompatible with something in your system. If possible, you could check the Event Viewer to find out what happens.

• Go into Control Panel, and ensure "View by" is set to "Small icons" or "Large icons". "Category" won't work.
• Click "Administrative tools", and then Even Viewer. In the left pane, expand "Windows logs" and then click "Application".
• Give it some time to load, and find a log entry pertaining "left4dead2.exe" (or whatever L4D2 calls its executable, 'cause I'm just guessing that name there). A tip is to just invoke the problem you're experiencing, note the time down to the minute, and look for the log entry in the Event Viewer sorted by time.

There have been issues like this with other pcs as well. What we know is this; the game plays for 20 minutes and then dies because of space that is not being "closed" (removed so the computer senses about 60gbs of map instead of the normal 1 gigabyte), additionally the game will sometimes stop due to a certain animation or effect ie. shadows on buildings or a back stab. This is just because the game was loaded incorrectly or has a flaw in the system.