I've seen this if the network card isn't recognised (watch carefully and you may see a message appear before Ghost client starts to this effect). If you're using an old version of Ghost, you might need to download the NDIS driver for that network card and create a Ghost boot floppy with it.
If you're using a newer version of Ghost that uses the 32bit Ghost client then you can create a Windows PE CD using the WindowsAIK and include the Ghost client on it. Windows PE includes loads of drivers.
If these PCs are the same type as the ones that are working then perhaps their NICs are having problems negotiating link speed/duplex with the switch. Try setting a particular port on your switch (presuming you're ghosting them on a separate LAN) to 100Mbps statically and a different one to Auto Negotiation. Then try it the affected PC on both ports and see if it works on one rather than the other.