The DHCP server is not available is the most likely cause of the issue where a new computer is unable to ping the default gateway. DHCP stands for Dynamic Host Configuration Protocol, which is a network protocol that automatically assigns IP addresses and other configuration parameters to clients on a network. The default gateway is the IP address of the router or device that connects a local network to other networks, such as the internet. Pinging is a network utility that tests the connectivity and reachability between two devices by sending and receiving echo packets. If the DHCP server is not available, the new computer will not be able to obtain an IP address or other configuration parameters, such as the default gateway, from the DHCP server.
This will prevent the new computer from communicating with other devices on the network or the internet, resulting in ping failure. References: [CompTIA Network+ Certification Exam Objectives], What Is DHCP? | How DHCP Works | SolarWinds MSP