Do you own the domain name 168vps.com? If you do, then you can use them as your nameservers, but you'll need to setup a zone file for the domain wherever you want, and then at the registrar set up a zone file for the domain. Then you'll need to set up the A records for the nameserver both in the zone file and at your registrar. Currently 168vps.com is registered at Xin Net Technology Corporation and the listed nameservers are ns1.oray.net, and ns2.oray.net, but that nameserver doesn't have an a record for the domain (it does have an SOA record).
Jeff