Weird DNS problem

I'm using domain network with Windows Server 2008 R2, domain name for example is mycompany.com.vn. I have some problem when reslove some websile, like Amazon.com, google.com. I use nslookup and it returned this log:

> amazon.com
Server:  secdc.mycompany.com.vn
Address:  10.71.1.2

------------
Got answer:
    HEADER:
        opcode = QUERY, id = 22, rcode = NXDOMAIN
        header flags:  response, auth. answer, want recursion, recursion avai
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        amazon.com.mycompany.com.vn, type = A, class = IN
    AUTHORITY RECORDS:
    ->  mycompany.com.vn
        ttl = 3600 (1 hour)
        primary name server = secdc.mycompany.com.vn
        responsible mail addr = pridc.mycompany.com.vn
        serial  = 17762
        refresh = 900 (15 mins)
        retry   = 600 (10 mins)
        expire  = 86400 (1 day)
        default TTL = 3600 (1 hour)

------------
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 23, rcode = NXDOMAIN
        header flags:  response, auth. answer, want recursion, recursion avai
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        amazon.com.mycompany.com.vn, type = AAAA, class = IN
    AUTHORITY RECORDS:
    ->  mycompany.com.vn
        ttl = 3600 (1 hour)
        primary name server = secdc.mycompany.com.vn
        responsible mail addr = pridc.mycompany.com.vn
        serial  = 17762
        refresh = 900 (15 mins)
        retry   = 600 (10 mins)
        expire  = 86400 (1 day)
        default TTL = 3600 (1 hour)

------------
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 24, rcode = NOERROR
        header flags:  response, want recursion, recursion avail.
        questions = 1,  answers = 1,  authority records = 0,  additional = 0

    QUESTIONS:
        amazon.com.com.vn, type = A, class = IN
    ANSWERS:
    ->  amazon.com.com.vn
        internet address = 203.162.71.197
        ttl = 943 (15 mins 43 secs)

------------
Non-authoritative answer:
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 25, rcode = NOERROR
        header flags:  response, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        amazon.com.com.vn, type = AAAA, class = IN
    AUTHORITY RECORDS:
    ->  com.com.vn
        ttl = 884 (14 mins 44 secs)
        primary name server = ns1.netnam.vn
        responsible mail addr = hostmaster.com.com.vn
        serial  = 2012031200
        refresh = 16384 (4 hours 33 mins 4 secs)
        retry   = 2048 (34 mins 8 secs)
        expire  = 1048576 (12 days 3 hours 16 mins 16 secs)
        default TTL = 2560 (42 mins 40 secs)

------------
Name:    amazon.com.com.vn
Address:  203.162.71.197

Sometime this worked, sometime this not. But when I change to public DNS, it works normally. I don't know how can I load those site with my network DNS.

Sorry about my bad english.