According to the Dell website, your monitor should do a maximum resolution of 1024 x 768, Documentation

So I'm wondering if it's a graphics driver issue with Windows. Can you try reducing the refresh rate in the display options and see if that gets you a higher max resolution?

Wow, I am feeling a little dim right now! I noticed the slider was at the far left (lowest resolution) but it wouldn't move to the right. I changed the colour quality to medium and then presto, it allowed me to change the resolution to the far right! I put colour quality back at 'high' and it still works. Thanks so much!!! So kind of you to do all that checking for me, Ruth.

Bingo! Thought it might be something to do with the graphics driver. Q.E.D.

Thanks Ruth this help me too I did same thing. I Have a Toshiba

Ah cool, fantastic stuff! I'd guess that the vast majority of flat screen monitors would be at least 1024 x 768, especially given the time that they were first brought out (around the millennium) when most graphics cards had enough memory to do at least that resolution.

The exception these days though being the new generation of "mini-notebooks", e.g. the Asus Eee-PC, some of which only have an 800 x 600 screen.