This is a well-known issue with the old HP 2xxxM series monitors, unfortunately. This practically ruins the HDMI port on the monitor. If you buy a DVI to HDMI adapter it will remedy this issue, but you will not be able to use the built-in speakers.
I haven't pulled mine out in years, so I cannot remember if this will work (I know I never fixed this issue) but I found this elsewhere:
Go to HP Monitor Menu - Image Control > Custom Scaling... Here, you see fit to screen greyed out and only 'Overscan' be selectable. Here is where it is unclear!! Press 'OK' button while 'Overscan' is selected. You will see 3 options: Auto, On, Off (Auto may be selected by default). Move this to 'Off' and your screen would automatically adjust to the right size.