whenever i play game, i right click on the desktop, click Personalize, then change it to Windows Classic under Basic And High Contrast Themes
i had that same issue til i started doing that
Win7 likes to take up a lot of RAM and whatnot to run right, and that doesn't mash well with some games i guess, not sure
but it changes your theme to like the old theme Windows had forever ago and takes up less memory
just change it back when you're done playing
shouldn't be an issue