Windows – Font/display all of a sudden too large

I use Windows 7 at work and have a two-monitor setup. All was well Friday afternoon, but this morning when I logged in, the computer decided it was time to switch my primary screen to the secondary monitor, and everything looked bigger on both. I switched the screens back to their proper positions and the font on the primary screen (the one with the start button at the bottom) is now okay. On the secondary screen, everything is too big – it seems that the display itself is too large, rather than the font size simply too large. When I move an item from one screen to the other, it's as if someone has put a magnifying glass on the second screen and the whole item expands and some of it gets cut off. I've gone into control panel and have set the font at 100%, and it won't let me go any smaller. Resolution is set at the highest level. I am not an administrator, and the above actions are about the limit of my computer know-how. What to do? Thanks in advance, superusers!