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First thing is first. I'd run wireshark on both the client and the server to see that:<br />
<br />
1) The client requests a DHCP address when using &quot;ipconfig /renew&quot;<br />
<br />
and <br />
<br />
2) The server is at least receiving that request.<br />
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I make this suggestion under the assumption that you have indeed checked the firewall and service already as you stated above, so I am skipping those basic steps.<br />
<br />
-Cliff<br />

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What is the lease time? &nbsp;Maybe all the addresses are leased out?<br />
<br />
I recommend 4 hour leases in just about all situations. &nbsp;The overhead is low enough and the problem of running out of addresses due to long leases is eliminated. &nbsp; Or, if keeping the &quot;same&quot; dynamic(?) address is important then maybe a bit longer lease time OR assign reserved IP addresses on the DHCP server according to MAC address. &nbsp;Most DHCP servers can do this.
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And, how many addresses are in the DHCP pool?
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pool: 192.168.1.10 - 254 are all open. DHCP is not handing out addressed to any device. There are no leases right now.<br />
<br />
I haven't tried wireshark yet. 
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There are some things that will &quot;kill&quot; DHCP on SBS including enabling hyper-V (not supported), or enabling a second NIC can do it sometimes. SBS only supports 1 NIC, all others must be disabled, not just disconnected. Also is there any third party security software installed; Symantec, AVG, etc.? 
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Thany youfor the quick reply. I'm going back onsite tonight to continue troubleshooting and will check out your suggestions. 
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I ran the &quot;fix my network tool&quot; and it reconfigured DHCP but it's still not handing out addresses to any PCs on the network. <br />
The firewall is off, I've checked for any software that could be causing a problem, only one NIC is enabled on the server. 
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A couple of troubleshooting tests you can do:<br />
-Try running on a workstation the DHCP Locater tool DHCPLoc. It is part of the resource kit or you can download from:<br />
<a href="http://www.petri.co.il/download_free_reskit_tools.htm" rel="ugc">http://www.petri.co.il/download_free_reskit_tools.htm</a><br />
At a command line enter &nbsp;<br />
&nbsp; &nbsp;DHCPLOC &nbsp;&lt;the work station's IP&gt;<br />
and hit enter (may have to hit enter twice). You will be prompted to enter d, q, or h. Enter d for discover (again may have to hit d twice). It should return the IP of the DHCP server and an offered DHCP address. DO NOT run this on the DHCP server itself, it can damage or disable the DHCP service.<br />
DHCPloc syntax:<br />
<a href="http://technet.microsoft.com/en-us/library/cc778483.aspx" rel="ugc">http://technet.microsoft.com/en-us/library/cc778483.aspx</a><br />
<a href="http://technet.microsoft.com/en-us/library/cc759117(WS.10).aspx" rel="ugc">http://technet.microsoft.com/en-us/library/cc759117(WS.10).aspx</a><br />
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<br />
-Another good test is to run Ethereal, if you are familiar with it, on the server, and filter out all but broadcast traffic, and then run the DHCPLoc tool on the workstation. See if WireShark picks up the DHCP request, and possibly tries to make an &quot;offer&quot;.<br />
<a href="http://www.wireshark.org/" rel="ugc">http://www.wireshark.org/</a>
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This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.
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I'm running &nbsp;SBS 2011 with 15 XP Pro workstations. Everything has been running fine for about 6 months but a few days ago one computer had the yellow ! and would not connect to the network. I configured a static IP and worked fine. The next day three more PCs had the same problem and the next day all of the PCs were not being assigned IP addresses. I rebooted the server, DHCP services are running, firewall is disabled, etc. I've set all of the PCs up with a static until I find a solution to the problem. 
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I'm running  SBS 2011 with 15 XP Pro workstations. Everything has been running fine for about 6 months but a few days ago one computer had the yellow ! and would not connect to the network. I configured a static IP and worked fine. The next day three more PCs had the same problem and the next day all of the PCs were not being assigned IP addresses. I rebooted the server, DHCP services are running, firewall is disabled, etc. I've set all of the PCs up with a static until I find a solution to the problem. 

SBS 2011 DHCP stopped handing out IP addresses

The Microsoft Server topic includes all of the legacy versions of the operating system, including the Windows NT 3.1, NT 3.5, NT 4.0 and Windows 2000 and Windows Home Server versions.

Microsoft Server OS

Small Business Server (SBS) is a line of server operating systems targeted at small businesses by bundling the operating system with a number of other Microsoft products that would normally need to be purchased or licensed separately. The most notable inclusions are Exchange, SQL Server, SharePoint and ISA/TMG (Microsoft's firewall and proxy server).