Right click on the Desktop --- click on Properties --- click on Settings tab --- now check your Screen Resolution most are going to be at a higher setting than 800x600 (which you probably have) so select something above that like 1024x768 and see whats best for you.
IF this does not work then ...... Click on the Start button on your Desktop -- go to Programs -- go to Accessories -- go to Accessibility Wizard and it will show you the options for disabled people that have vision problems. You can then follow the prompts to change it back to normal.
IF it's a problem that Eemckinney wrote about where it's your internet browser and you have a scroll wheel on your mouse...... Hold down CTRL and the Windows button together (CTRL+WIN) and scroll your mouse up or down and it will use the auto-zoom to adjust it to a correct display.
On the lower right hand of the screen if it is just the internet should be a zoom lens if it is at 200% or even 150 its to much just reset it to 100%. If its actually your computer you will have to go into go into your control panel and reset it.