You can check your DNS servers by going to a CMD window (Windows Key + R -> Type in: CMD hit OK) and type in: ipconfig /all. You will find the DNS under the DNS Server entry for your device.
To check if the DNS servers are working type in: Ping Google.com
You should get a return similar to the one below which includes the IP number for Google.com if not your DNS servers are not correct.
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
Pinging google.com [22.214.171.124] with 32 bytes of data:
Reply from 126.96.36.199: bytes=32 time=41ms TTL=56
Reply from 188.8.131.52: bytes=32 time=67ms TTL=56
Reply from 184.108.40.206: bytes=32 time=90ms TTL=56
Reply from 220.127.116.11: bytes=32 time=113ms TTL=56
Ping statistics for 18.104.22.168:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 41ms, Maximum = 113ms, Average = 77ms