dhcp not working

Our DHCP server on SBS 2011 is not performing properly, on few workstations its not assigning the IP address, we have tried to reset the network card on workstations but they are able to obtain any IP and the workstation is set to public network for some reason, all was good earlier but this morning this suddenly happened to 3 of our workstations.

also on the workstation network adapter I saw its able to send data but receive is 0
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Steve McCarthy, MCSE, MCSA, MCP x8, Network+, i-Net+, A+, CIWA, CCNA, FDLE FCIC, HIPAA Security OfficerIT Consultant, Network Engineer, Windows Network Administrator, VMware AdministratorCommented:
I would verify your DHCP server is setup properly and that you have available addresses to give out. Verify your scope settings for DNS which should point to your SBS server

Generally, I setup 2 DHCP servers for fault tolerance and set them up almost identically. You have an SBS, so here would be my recommended setup.  So for example if my internal IP Addressing scheme was 192.168.1.x, I would setup the scopes to go from .1 to 254 and exclude, for example the ranges from .1 to .69. This is where I put all my static IP addresses.  Then I exclude, for example 70 – 99.  This is for future use should I need to free up 30 more addresses later for DHCP addresses. Finally, I would hand out addresses 100-177 and Exclude 178-254. Open up the entire Scope if you need it.

Finally, on the DHCP IPv4 properties, under the DNS tab, Ensure that “Enable DNS dynamic updates………” is checked, as is “Always dynamically update DNS records”.  You also want to check, “Dynamically update DNS records for DHCP clients that do not request updates…….”

If you have a switch in the middle, it would not hurt to pop that and reboot that server.
Mal OsborneAlpha GeekCommented:
Do you have a managed switch? If so, check the spanning tree settings. If you are running the older STP protocol, the port will be blocking for a while, and often this prevents DHCP from working. Disabling STP or configuring RSTP will fix this.

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How exactly is your network laid out? However, I'd be checking the number of DHCP addresses available for lease, along with the length of leases that's set as well. I'd also check to see if there any issues with your network equipment.
If you are having DHCP issues, one quick check to rule out a problem is to check DHCP is running.  

It may sound silly at first, but sometimes people plug in another device doing DHCP such as a router from home.  If this happens, Windows DHCP sees that another DHCP is running and stops. (with an event inthe event log that is easy to skip past)

Then wither the rogue dhcp is removed when the user realises they can't do what they wanted, leaving you clueless, or it gives out IP addresses possibly on a different subnet.

PC's that already have a lease may continue to use it, leading you to think DHCP is running when it isn't.  

so just a quick check that DHCP is running is a good idea.  Just open DHCP console and see if there is a red X
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