External monitor has wrong resolution

I have a 23' external monitor (through VGA) which always worked at 1440×900 and looked amazing. Today after I unplugged it, it still says it's working at 1440×900 but it's actual resolution is bigger.

I've tried unplugging, rebooting, Detect Displays, change res. and change back but no dice. Any clues on what might be happening?

Thanks!