Conflicts

Our company bought some computers that have 3Dfx and sound cards installed. The sound card and ISA type an 3Dfx is placed on PCI. The video card is placed on PCI too ( Voodoo on PCI 2, video on PCI 1, sound card on ISA 1)
If i let the sound card onISA 1, Windows won’t detect the 3Dfx.
If I put the sopund card on ISA 2, windows won’t detect the sound card , but I have the 3Dfx.
If i put the sound card on ISA 3, both of them will work.
Do you have a logichal explination for this ?
When isay “Won’t detect” i mean Windows doesn’t realize the card is in the computer. All components are plug’n’play !