Why can't my flat panel monitor display thisvideo mode?

I just got a new lcd flat panel monitor but when I plug it in and turn it on it says it cannot display this video mode. How can I fix this? It is a Dell Ultrasharp if that matters. Thanks in advance.

plug in your old monitor, change the resolution to 800x600 then go back to the ultra sharp and see if that works? maybe change the refresh rate too just in case, make it 60GHz

YOUR VIDEO CARD MAY NOT SUPPORT THE MODE YOUR LCD RECOMMENDS.USE THE NEXT BEST MODE.TRY THE AUTO SETTING FEATURE IN THE LCD AND LET THE LCD DIAL IN TO THE VIDEO CARD FOR THE BEST POSSIBLE MODE THAT THE CARD WILL SUPPORT.

my gateway lcd screen does that too( i got it for free), change it to 1024x768 and 60 hertz, it should work