Maybe you have changed the setting for the screen? If you push Fn + - (both printed in red on my key board) it should minimize the letters smileys/smile.gif
what browser are you using? The two things that come to mind are:
1) zoom level.
In Firefox go to your menu click View>Zoom>Reset
In Chrome View>Actual Size
In Internet Explorer (which is from the devil) if you have a wheel mouse you may have accidentally pressed the ctrl button while moving the wheel which would zoom in or out.
2) Accessibility settings: I've seen this happen before and it can be frustrating. On Windows it is called "Magnifier" where it creates this magnifying glass type of effect. Maybe it is useful if you have very poor vision... Mac also has something like this in "Universal Access" but it is more of a traditional zoom in / out. In windows click the Start button>Programs>Accessories>Accessibility.
Click Magnifier