SOLVED 2008 Mac Pro no video display until login, no video display when booting off DVD

[Fishmonger]

I've just bought a 2008 Mac Pro, which runs Lion. I've noticed that it doesn't send input via HDMI or DVI until it's loaded the login screen, then the inputs work. I've also noticed that it doesn't send video input when booting off the Snow Leopard install DVD, and installing Snow Leopard is why I bought the damn thing.

Any ideas on how to fix this? I've seen nobody else talking about this problem.

 

[Fishmonger]

Turns out the ATI Radeon shipped with the Mac was in fact the PC variant, and did not have the software to view EFI/Boot or anything that doesn't directly support the card. (10.6.8 is the first version of Leopard to support Radeon 5770, whilst my DVD is 10.6.3)