I have an Optiplex 980 with two ATI Radeon HD3450 cards, with the card in Slot 1 supporting two monitors, and the card in Slot 3 supporting one monitor. The BIOS Video was initially setup to Auto. Upon boot, the two monitors coming off of Slot 1 would display the Windows 7 startup splash screen. However, once the boot process completed, the login screen would display on the monitor supported by the video card in Slot 3. The two monitors off of Slot 1 would go to sleep, since they no longer were receiving a video signal.

I set the BIOS video so that it was no longer in Auto, and that the card in Slot 1 would be the default. However, no change.

The only way that I can get all three monitors working after logging into Windows, is to 'uninstall' the video cards from the Control Panel - Devices, then do a "Scan for Hardware changes". The system will then detect all three monitors; after that, I have to configure the Displays so that the two monitors off of Slot 1 are setup as "Extend my desktop onto this display".

I'm out of ideas. Hoping someone else has seen the same problem and discovered a fix.