I recently upgraded my monitor. My old one had a native resolution of 1680x1050, and my new one has a native resolution of 1920x1080. KDE 4.3 worked fine on my old monitor, but on the new one, the login screen doesn't display correctly, and my taskbar only stretches across 1680 pixels. I already reconfigured X, and it didn't help. How can I fix these display issues?