If the game keeps running in the background when you get kicked to the desktop, it's most often because your computer is doing something it considers more important than your game.
That "highly important task" may be any program checking for an update, or automatically updating itself. Anti-virus or any anti-xxx is often the culprit, some are worse than others. Besides updating, they may also do other maintenance chores. Flashplayer, Java, Steam, Real/QuickTime/Whatever-player, the automatic update checker of your computer or printer... Any of those will check for updates on a daily basis by default.
An "easy" fix? It will take some time and effort, but it's not rocket science. Start by looking at the lower right corner of your desktop and take a close look in the Taskbar icons. Each of them is a sign of a running program. Some may be hidden behind the small triangle. Right click each of them and look for "Settings" or "Preferences". Find the update settings and set them to manual. You may feel safer if you leave the Anti-xxx to automatic, though. For the Anti-xxx, look for other automated tasks such as "System Optimizing" and other Windows related tasks. Either disable them or set them to be done by request only, i.e. manually. Especially Norton can be a nuisance in its eagerness of doing regular maintenance.
Next look at the Start menu programs list. Look for folders named after the brand of your computer, printer and other gear you've installed. If there's an updater, open it and check the settings. Set them to manual.
In the Control Panel you'll find at least Flash and Java, again open them and set the updates to manual.
"Manually" can be said in other words, too. "Automatically check for updates - Never" means the same.
Don't leave Skype running in the background either. I like to have it automatically starting, but before starting the game I right click it and shut it down.
There's a bunch of other things you can do to reduce the background activity.
http://www.blackviper.com/ is a very thorough source for information.
