Katie, ignore the Configure your Desktop settings.
I would suggest using the Configure Your Computer (PCC) as in your picture above.
Change the monitor to generic 1280x1024,
Change the Res to the same setting 1280x1024.
When both have been changed accept the new settings and reboot when instructed.
If you do the above and nothing else, please confirm the settings in PCC immediately after the reboot.
It *should* have retained the new settings, but we need to be sure.
If you have success with that then better monitor & resolution settings can be tried.
Highest preset resolution 1280 x 1024 at 75 Hz
Highest addressable resolution* 1600 x 1200 at 65 Hz
The above indicates there might be some limitations on the highest resolution .... can you give an indication what the '*' refers to?
* Addressable means the monitor will sync up to this mode. However, Dell does not guarantee the image will be sized and centered correctly.
Dell guarantees image size and centering for all preset modes
which includes 1280x1024
Apparently this is a 15" monitor
Displaying brilliant images at a maximum resolution of up to 1280x1024 pixels,
Diagonal 382.8 mm (15.07 inches)
Because of the size of the display, and Dell's 'warning', I would not attempt going higher than 1280x1024.