if host aggregate is not set VM are created in default availability zone and there may not enough resource to launch the VM . set host aggregate /availability zone for new compute and use same availability zone while create new VM.

on many occasions network miss configuration on new compute lead to this issue.please check network part on new compute.

/var/log/nova/nova-compute.log will point the issue on compute node.

check all node (block, object, controller, existing compute) are resolving from new compute and visa-versa.

Regards, Ajay

Is your nova-compute service running fine on the new compute node [check the /var/log/nova/nova-compute.log on compute node]

Check nova service-list [after sourcing appropriate keystonerc file for admin] compute service should show enabled and up

Have you configured the additional compute node as different host aggregate / availability zone - then in the /etc/nova/nova.conf ensure you have AvailabilityZoneFilter added for scheduler_default_filters ; and then while launching the instance select the appropriate availability zone.

regs, nd