While my computer was off, I unplugged the monitor's HDMI cable and plugged it into another computer. I then forgot it was unplugged and started up my openSUSE computer. When I plugged in the cable, it was missing the correct resolution of 1920x1080 and only allowed up to 1600x900. So I restarted and it now showed 1920x1080 but the image is too big for the monitor - the taskbar is off the screen and the titlebars of the windows are too far beyond the top of the screen!

How do I get this to properly match up to my monitor again?