The issue when a phone is stuck on Sending DHCP requests means that the phone is unable to receive an IP address from your router.

First of all, make sure the Internet cable is connected to the NET port on the back of the phone. Connecting it to the PC port will NOT work.

A DHCP server is almost always provided by a router which provides IP addresses to devices such as computers, and phones. All devices must have a valid IP address in order to connect to a network, and further to the Internet. 

1. Your router is not providing IP addresses.

i. Your router ran out of IP addresses in your IP addressing pool.

You can either change the subnet to provide more IP addresses or lower the lease time in order for old IPs to expire.

ii. Your router needs a reboot.

Sometimes routers get stuck, especially in high traffic operations. It's usually a good idea to simply reboot the router by unplugging the router for a few minutes and re-connecting it.

2. Defective cable

Replace cable leading to the phone.

3. You are not using a DHCP server, and are assigning IP addresses manually.

Simply press the X [Cancel] key several times, until the Sending DHCP requests terminate.

Once passed the screen, you can manually press the configuration button and configure static IPs.

4. You connected it to a switch but the switch is not connected to a router.

Occasionally a switch is needed in order to provide additional phone ports. This switch needs to be connected to the router in order to provide IP addresses. Follow the cables until you find the correct cable leading to the router, and connect it.