Checking out the PDF version of your manual.
<b>AGP Frequency Selection (AGPFS)</b> next to your ide cable connection on your motherboard, this is a jumper that selects either 2/3 ratio or 1/1 ration between your CPU front side bus (FSB) speed and AGP speed. If your cpu FSB is running at 100hz then it should be selected at 2/3 ratio, pins 1 and 2 shorted or jumpered across. If FSB speed is at 66hz then it should be selected for 1/1 ratio pins 2 and 3 shorted. Let us know how this is configured. What CPU do you have in your machine? This will affect this setting, I need to know in order to help. Now the VooDoo doesn't use AGP transfers so it is possible that this is configured wrong allowing the Voodoo to work but not the Radeon which does require AGP transfers.
<b>Some Bios settings:</b>
1. Standard CMOS Setup
<b>Video</b> set to <b>EGA/VGA</b>
2. Bios Features
<b>PCI/VGA Palette Snoop</b> set to <b>disabled</b>
<b>Video ROM BIOS Shadw</b> set to <b>Disabled</b>
3. Chipset Features Setup
<b>Graphics Aperture Size</b> set to half of your memory or <b>64MB</b>
<b>Video Memory Cache Mode</b> set to <b>UC</b> new setting for me, something similar on Via boards which doesn't seem to do anything for the Radeon.
4. Power Management (long shot but just maybe)
<b>Video Off Option</b> set to <b>Always On</b>
5. PNP and PCI Setup
<b>PNP OS Installed</b> set to <b>Yes</b>
<b>Slot 1/2/3/4/5 IRQ</b> all set to <b>auto</b>
One more thing, if your first pci slot next to your AGP slot has a card in it, move it to another slot. Reason is because the first pci slot shares an IRQ with the AGP slot (Radeon). Sometimes the Radeon just doesn't want to share an IRQ. So keep that slot empty for now.
<b>VGA Bios Sequence</b> set to <b>AGP/PCI</b>
These seem to be the most applicable settings in the bios for proper operation of the Radeon. You may have to install your Voodoo to set, just the bios section that is. Do need more info as in CPU, amount of memory, operating system, installed cards etc. It is hard to figure out what you have and don't have which could cause conflicts. Good luck and let us know.