Windows 7 Monitor Problems

I have installed Windows 7 on my Dell Dimension 2400 PC (I know a few years old) . However, the resolution on the monitor has changed to default to 600 x 400 making the images appear very large. I can change the resolution to 1048, but this results in the appearance being very fuzzy and unable to view the borders of windows (the border is completly black, so for example I am unable to see the mimimise, maximise and close icons are in the top right hand corner).

I have installed all the necessary drivers and this has not resolved the issue.

As a result, the only clear way to view programs is to revert back to 600 x 400, but this does not allow add-ins such as cameras to work as it requires 1048.

Has anyone else encountered this, or is there a solution available?

Thanks