How do I switch off Multiple Monitors ?

I have a Dell Inspiron 5150 with a NVIDIA GeForce FX Go5200.  I am trying to increase my screen resolution higher than 1024x768. However, the Multiple Monitor feature is showing in my display settings even though I do not, and never have had, another monitor connected.  I can not not turn this feature off, so I can't change the resolution.

Can anyone help please?