Article ID: 331796 - Last Review: March 4, 2011 - Revision: 28.0
Perform a clean startup to determine whether background programs are interfering with your game or program
This article describes how to start your computer by using a minimal set of drivers and startup programs so that you can determine whether a background program is interfering with your game or program. This kind of startup is known as a "clean boot." This article also provides information that you can use to o troubleshoot application or service conflicts.
When you start Windows by using a normal startup, several applications and services start automatically, and then run in the background. These programs include basic system processes, antivirus software, system utility applications, and other software that has been previously installed. These applications and services can cause interference when you install or run a program, such as Microsoft Flight Simulator X or Streets & Trips 2010.
...more http://support.microsoft.com/kb/331796#appliesto
Applies also to many bother Microsoft games. See the link for more details. Solution varies by OS.
