Your games are probably running at 800x600, but rather than scaling the image to take up the full screen, your display is showing it at its native resolution (1 game pixel == 1 LCD pixel).
The first thing you'll want to try is increasing the video resolution in the game's options. According to Dell, the native resolution of your display is 1366 X 768.
Two problems you might run into:
- The game doesn't provide any options to change the resolution.
- Your laptop isn't powerful enough to run the game at a higher resolution, and performance suffers.
Most video drivers have a setting somewhere that controls whether to scale full-screen apps to the maximum size of the screen or to show them at the native resolution. If you can't change the actual resolution that the game runs at, you'll want to look for this setting somewhere in your display/video options and change it so apps will be stretched to full screen. (Note: This will probably look pretty ugly. LCDs aren't very good at this, which is why the option exists in the first place.)