Re: Inspiron 5110 and SE198WFP resolution mismatch
Try changing the Intel graphics driver's scaling option. Press Ctrl+Alt+F12 keys to open the driver's control panel. Select the external display from the drop-down list for 'Display'.
Check if you are able to change Scaling option to 'Scale Full Screen'.
Please check if you are able to change the resolution to 1366 X 768 after selecting the external display.
If this does not help, try to perform a factory reset on the monitor. You can refer to this link for the steps: http://dell.to/OsyJDV.
Do write back with the results.