What happens as the signal splits is actually somewhat more complicated. There are so many variables and differences in capabilities and signals of different devices, that most splitters are not designed to handle the situation. There is probably nothing wrong with the DVI splitter itself; the user needs to ensure that all the equipment is mutually compatible with each other and with the DVI splitter cable being connected to the signal's source.

A video card or other device must have the built in capacity to transmit a useable signal through the splitter. For example, the card may not generate a signal that can be split; multiple signals will have to be come through connections to different ports. Some devices or cards were never designed to supply a signal that can be split--they must specify that they have dual links.

If the output devices do have the capability to generate a signal the signal sent from them must be one that is compatible; that is, the sending and receiving devices must both use either digital or analog--cannot mix them. For a signal source that is analog, both the receiving monitors must be analog also.

If you try to send a feed from a card that still uses analog signal to a digital screen via your new DVI splitter cable, or to one analog and one digital screen, it will not do it. If this is exactly what you want to accomplish, there is, happily, a solution. You need to check out DVI converter boxes. It will save you the concern of figuring out who is analog and who is digital by converting the device's signal as needed during transmission.