Hi@akhtar,
 You should change the default quota limit for booting the new instance. To view the default quota limits, run the below command.
[root@localhost]# nova quota-defaults
+-----------------------------+-------+
| Quota | Limit |
+-----------------------------+-------+
| instances | 10 |
| cores | 20 |
| ram | 51200 |
| floating_ips | 10 |
| fixed_ips | -1 |
| metadata_items | 128 |
| injected_files | 5 |
| injected_file_content_bytes | 10240 |
| injected_file_path_bytes | 255 |
| key_pairs | 100 |
| security_groups | 10 |
| security_group_rules | 20 |
+-----------------------------+-------+
The below command will allow you to set new quota limit.
[root@localhost]# nova quota-class-update --instances 35 default
[root@localhost]# nova quota-defaults
+-----------------------------+-------+
| Quota                       | Limit |
+-----------------------------+-------+
| instances                   | 35    |
| cores                       | 20    |
| ram                         | 51200 |
| floating_ips                | 10    |
| fixed_ips                   | -1    |
| metadata_items              | 128   |
| injected_files              | 5     |
| injected_file_content_bytes | 10240 |
| injected_file_path_bytes    | 255   |
| key_pairs                   | 100   |
| security_groups             | 10    |
| security_group_rules        | 20    |
+-----------------------------+-------+
Hope this will help you.
Thank You