What to do if my dhcp client is not getting ip from dhcp server ?

This behavior may be caused by one of the following scenarios:

Scenario1

Changed IP address on DHCP server and now clients cannot get IP addresses.

Scenario2

DHCP clients across router from DHCP server are unable to get an address from the server.

Scenario3

Multiple DHCP servers exist on the LAN.

To resolve each possible cause, use one of these solutions:

Solution for Scenario1

A DHCP server can only service requests for a scope whose network ID is the same as the network ID of its IP address. 

Make sure that the server's IP address falls in the same IP network ID as the scope it is servicing. For example, a server with IP address in the192.168.0.0 network cannot assign addresses from a scope like10.0.0.0, unless superscoping is used. 

Solution for Scenario2

 A DHCP server can provide IP addresses to client computers spanning multiple subnets if the router that separates them can act as an RFC1542 (BOOTP) relay agent. 

Configure a BOOTP/DHCP Relay Agent on the client segment. This can be the router itself or a Windows NT computer running the DHCP relay service.

Configure a DHCP scope to match the network address on the other side of the router where the clients are. Make sure the subnet mask is correct. - Do not configure a default gateway on the DHCP server's NIC such that it is the same address as that of the router supporting the subnet where the clients are. - Do not include that subnet's scope in any superscope that is configured on the DHCP server's LAN segment.

Make sure there is only one logical route between the server and the remote clients.

Solution for Scenario3

Make sure that you do not configure multiple DHCP servers on the same LAN with overlapping scopes. 

In case of Small Business Server, the DHCP service will automatically stop when it detects another DHCP server on the LAN.

This is common case, you can follow the steps to troubleshoot

1. Normally, DHCP IP providing from Router and Access point is bridge. So you can verify with wired cable to your laptop. If you are getting IP Address from wired cable, router is releasing IP Address and not related  to DHCP scope issue. [Drill down first - IP Releasing from Router]
2. Check any of the other device getting IP Address issue from WiFi Access Point then WiFi Access point occupied with maximum connections. So you want to restart your Access Point. [Drill down - WiFi Access point limit reached]
3. Before restarting the router, verify with same range static IP Address on your network interface and test the connectivity to Local/Public Network. [Drill down - WiFi Access point communication from Laptop to Router]

Following cases will give clear picture about your network communication and it will vary the troubleshoot steps depends on your network. Example: If you have multiple WiFi Access points then chances of WiFi Signaling issues, or multiple dhcp scope servers on network, etc.

-relase this ip from DHCP scope and then release it from pc and renew it again 

- be sure that this PC connecting to DHCP server

- disable/enable network card

Make sure the connection between dhcp client and dhcp server using ip address

if the DCHP server is configured & running & physical connectionis ok :-

1- all of  IPs in the scope are used

2- another DHCP Server or " Service" in case if you are using a router or Access point to Distribute IPs " is running.

3- firewall may block the request

4- IP add for the DHCP is not in the same Network ID of the Scope you are assigning IPs from

check your dchp range on the router, ensure that it has been activated, and if all is done then ensure that the client is dhcp enabled not static.

Please explain your setup more. What router are you using? Has this router got sub interfaces setup and DHCP scopes asigned to each sub interface?

Is this feeding a switch which is then feeding the access point or is the access point plugging direct into one of the ports on the router?

If the access point is plugging straight into the router, then try plugging your laptop direct into the router and see if it is able to pick up an address, if it does successfully then you know the Access Point is the problem.

If it doesn't then probably due to misconfiguration on the router. Plug the laptop into another router you know does work and see if it picks up an address to rule out that the problem is with the laptop.

may be the cause duplicate ip and may conflict happen. or else your conectivity problem,one of the file may miss from the flz forward lookup zone or reverse  lookup zone else . may that your system out of the scoops while you assigning the schope the same scoope you use to the dhcp.

Thanks guys. Actually the scenario is they are using accesspoint for the wifi router. Where will be the problem ? From the router or accesspoint ?

Most common reasons are;

1. All available IPs are issued already and every issued IPs are active.
2. Client PC might not be listening on port68 for any reason.
3. Client PC might not be configured to automatically receive IP from DHCP server.

check the dhcp scope range  it possible that number of IP not enough for all devices