Contact Compaq perhaps and see if they will help… They or the original vendor may possibly help – but likely they will require some proof of ownership to back up your story.
Sadly more than a few come to forums seeking help with kit they have acquired – one way or another, legally or otherwise… Not being able to truly separate genuine from stolen… most forums tend to decline to help directly – other than to suggest contact previous owner or vendor. Or go hunt on the internet in general for an assortment of hacks…

If it’s the actual windows logon… answers on the web a plenty to resolve that; and of course you could simply reset/restore it to factory state…

Look for a reset button on the monitor itself (usually under the screen or on the front).
Or use the monitor’s built-in image-adjustment buttons – – – width, height, vertical position & horizontal position.

Read the monitor user guide on how to use those buttons, or download it from the manufacturer’s website.