1. Uninstall the drivers of your current video card.
2. Turn off the PC.
3. Remove the card, connect the monitor to the integrated one.
4. Turn on the PC, log into the OS.
5. Uninstall drivers of the IGP.
6. Turn off the PC.
7. Insert the card, connect the monitor to it.
8. Turn on the PC, go to the BIOS settings and disable your IGP. (Read the motherboard manual to find out, how to do all this.)
9. Save new BIOS settings and log into the OS.
10. Install drivers for your videocard.
CPU: AMD Phenom II X4 810 @ 3120MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 835/1135MHz | Display: L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 3.11 Pro x64