Monitor goes to no-input randomly after start

Hello,

I'm running windows XP, with a new mobo (Asus M4A78 PLUS), and my old Diamond Viper 1 gig ATI Radeon HD 2900XT graphics card. The graphics card is the only support for the monitors, 2 dvix outputs.

Everytime I turn on my computer it starts up, and within 30 seconds or so the monitors go to no-input. Sometimes it makes it to windows in which is says no multi-monitor support.

I tried with just one monitor but the same thing happend 30 seconds or so then off. When the computer warms up it seems as soon as "windows" boots from startup it goes to no input.

It seems the computer is running very slow like it's over computing, sometimes I will get in long enough to run Catalyst Control and configure the monitors and it speeds up greatly, but still within a few minutes it will go out of range. I tried all sorts of drivers... what's the problem?

Help me.

Dan