Hi Javier,
It sounds like the VGA driver is either missing or not properly installed. Since you mentioned that there is only an SVGA controller chip on the motherboard and no dedicated graphics card, it's likely that the driver is included with the installation disc of the machine.
Here are a few steps you can try to resolve this issue:
1. Insert the original software installation disc into the computer.
2. Open Windows Device Manager by pressing Windows key + X and selecting "Device Manager."
3. Look for any devices under the "Display adapters" category. If you see a generic VGA adapter or a device with a yellow exclamation mark, it indicates that the driver is not installed.
4. Right-click on the display adapter and select "Update...