I don't see that model on the proview web page. Is there any other model number? I did a search and see that model mentioned, but can not find it on the proview web site in order to get the user's manual.
Is it anything like this monitor?http://www.proview-g..._UM.aspx?sn=378
If so, on the third page there is the information about setting the horizontal size. You would need to press the menu button, then use the arrow buttons on the monitor to select the proper icon and then press the menu button again to select that option. You might look to see if there is another monitor which is close to yours. It seems that proview does not like to keep information on the older monitors or there is more to the model number.
You might also need to ensure that the settings are compatible with the monitor. Something the refresh rate can exceed what the monitor can deal with at a given resolution.