What would you do if your clients are not taking IP from your DHCP server?

Client Machine is not taking IP Means, Maybe DHCP Clinet is not running or  Network Drivers Problem or DHCP Scope is full ( I.e Server don't have IP to give Client ) or May be LAN Port or CAble problem. to take event View logs and anaysis

1. Check the physical connectivity of client computer (cables and network adapters) 

2. Use PING command for checking connectivity with dhcp server.

3. DHCP SCOPE is full.

4. We can analysis in event view logs.

1. Try to ping DHCP Server - If not reachable no response via PING do 2nd Step

2. CMD > Ipconfig \\release and then Ipconfig /renew and Ipconfig/flusdns to remove scale records that can fix the issue

3. Restart the Computer  - If Still the issue is not resolved Ping the Loop Back IP : 127.0.0.1 and unistall and reinstall the Network Drivers - still issue exist.

4. try to use other LAN Port whether its Providing IP or Not .

Check the DHCP service.

Check if the DHCP server is authorized to assign IPs. 

Check if the scope is in enable state.

Check if the scope has free IPs available to assign client computers.

I would suggest you first try the static IP method, just to see if the client really connects to your network and can transmit data, followed by a reboot of the AP, and finally a reset/readoption if needed..

If Multiple clients are not getting IP from DHCP Server provided it was before, then surely there must be an issue on the DHCP server side. It can be DHCP Server OS/Service level issue if running on windows or the server does not have any IP left to issue to the client or may be the administrator has accidentaly enabled or applied DHCP MAC filtering for all the devices using DHCP Server.

I will assign temporary IP address

are DHCP services are running correctly ?

are any changes happened in switches .. configration changed or IPHelper for example ??

is the scop full ?

are there changes happened on firewall roles ??

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may be some one connect router in the network and start to distribute IPs - this is more difficult to fine it.