DNS Testing / NS Lookup/Ping

How can i test that DNS is working properly?

When i do nslookup it finds my DNS Server

Default Server: DNS_Server
Address: 192.168.10.55

but if i put in the clients PC name in next i get a server failed message. Also if i do a ping -a it returns the ip but does not return the name. Is something wrong? What can i do to test things?