Multiple Monitor Issue

I have 4 identical monitors connected (Dell E1913). 3 of the 4 have settings:

Desktop Resolution = 1440 x 900
Active signal resolution = 1440 x 900
Refresh rate (Hz) = 60 Hz
Bit depth = 8-bit
Color format = RBS
Color space = Standard dynamic range (SDR)

and yet...the 4th monitor will not allow the above settings and screen is blurry! The settings on the 4th monitor are:

Desktop Resolution = 800 x 600
Active signal resolution = 800 x 600
Refresh rate (Hz) = 60 Hz
Bit depth = 8-bit
Color format = RBS
Color space = Standard dynamic range (SDR)

When I attempt to go into settings to change from 800 x 600 to 1440 x 900, the boxes are grayed out and will not allow me to change!

Previously all four monitors worked find until the other day. Can anyone give me some tips as to how I can change the 4th monitor? Thank you in advance.