Windows 2000 DHCP Hanging

I have a Windows 2000 DHCP server which is configured to serve a single address to a single PC over a vlan. The user gets on ok, but once they leave their machine cannot pull the address again (once the lease time is up). While checking the server I noticed that the address does not show up leased (in the lease window), but when I check the stats for the scope, it show that no addresses are available. Any ideas?

Cheers,

Mac