Disabled Network Adapter

I am working with a client that is having a problem with a network adapter. The PC is running Win2000 and sits on a small network. Every couple of days, the network adapter suddenly becomes disabled. I know it is not the adapter itself, because it is the second one I have put in. Unfortunatly, I have no other PCI slots available to move it to. I also tried to assign a new network device ID, but this did not help. Any ideas???