It appears that there is an IRQ conflict. Both cards are set to the same "channel", and thus are conflicting. You must find a jumper or dip switch setting for IRQ and set it to something that no other device in your computer uses. You need not worry about plug-and-play devices as they will auto-resolve their conflict. As to changing the IRQ settings, this depends on your hardware.
However, since you wish to add two disks, you only need one such card. You simply need an IDE cable with three connectors: one for the card, and two for disks. These are quite common.
CARD-------DRIVE 1(MASTER)-----------------------------DRIVE 2(SLAVE)
Make sure one of the drives is a master, and the other is a slave, or both use the Cable Select (CS) feature, as per their jumper settings. The order of master-slave on the cable doesn't matter if you aren't booting from wither of the drives, but if you are using CS, both drives must be in CS mode, and then they will automatically detect master/slave by their positions on the cable.