Like most other bits of hardware, monitors need drivers so that XP can translate a program's output to something that the hardware can understand. Modern monitors are plug-and-play and XP can load the correct drivers automatically.
Older monitors may not be able to do this, so you have to select the drivers. Right-click on a blank part of the desktop and click Properties - Settings - Advanced - Monitor - Proerties - Driver - Update Driver. Click No, not this time - Next - Install from a list - Next - Don't search - Nextand then go or a basic monitor. If the monitor is badged, you might find a specific driver for that make.