Monitor doesn't connect to the dell desktop with Windows XP.

[Ekfer]

Since then, I have not added nor modified any of the components.

Sent from my LGMS210 using Tapatalk

[magicniner]

Replace the BIOS battery and see what happens, there is always the possibility of a board level failure.

[Lee Roberts]

I would try the monitor on another PC/source as well just to be sure that works.

Before you change the bios battery, try simply resetting/clearing the bios first as the battery maybe ok and is usually the case.

There should be a small pin jumper typically located in the same area as the battery, you sometimes need to remove this jumper or switch its configuration, I normally power the system on and off on both methods, if you look up the manual for the motherboard it should tell you how to do it for that board and the locations.