old GF MX4000 - screen turns off after booting WIN XP

Hi folks, Got some old spare components, so I've decided to build a machine.. It's and old VIA KT133 QDI board, Athlon 900 CPU.. Got this GF MX 4000 VGA card and one even older GF2 MX card. Everything is workign just fine... I've maged to get the PC up and running, even WIN XP runs fine... but...only with the GF2MX card... when I put the GF4MX into it...well, the machine boots up, XP loading screen appears but just when the loading is complete and it is supposed to show the desktop the screen turns off like no video signal is present. I'm pretty sure it's not a driver issue cause the result was same with microsoft default driver and after installing nVidia driver. However, If I enable "VGA MODE" in XP, the desktop actually shows up...what might be the casue of this problem?

How could I possibly have both of them in the PC at the same time ? And why would I do that ? they're both AGP cards