Windows

I wonder if you have a limit number of IPs for distribuition. A network without a porxy or firewall will likely use real IP addresses and normaly, the number is limited.
If the above situation applies to you, check the leases on DHCP to see how many IPs do you have left. Likely, because of the default lease period is 3 days, and many processes requires an IP lease that will not be released for 3 days, you might be running short.
Solution, decrease the lease time to 1 day or even 12 hrs.
That will help you reclaim the IPs not been used on the network.

Good Luck!

check you scope. how many ip's do you have? are they all being used? if they are private (ex. 192.168.1.x-255) put any nic in your server and add another network (192.168.2.X-255) Also what kind of switch do you have. Dlink and some other had some boot up problems that would not let traffic pass through the switch until it was completely booted. This is bad b/c if you are asking for ip's at the same time too bad so sad.

Another thing is STA Spanning Tree Algorithm. This keeps traffic from coming into the same port that data came from. this keeps data from looping. Dlink and others have problems. Usually you have to disable it.

hope this helps.