PTCL broadband showing DNS error on browsing Youtube.com and FaceBook.com on Sunday, 27th March 2011. It seems some technical problem in PTCL DNS servers.
This issue can be resolve by changing DNS setting. For this you need to go to your “Network connections” at my network place. Right click on network connections and then click on properties. Now double click on internet protocol (TCP/IP) option. On opening internet protocol properties, if you are not using any manual IP address then select “Use the following IP addresses” and change your IP address setting to following
IP Address: 192.168.1.2
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.1.1
Now check on “use the following DNS server addresses” and set following addresses
Preferred DNS server: 203.99.163.240
Alternative DNS server: 202.125.132.12
and press ok. Now try youtube.com once again. Hopefully It will works but if problem still presist then call PTCL @1218 and follow formula of SUB KEH DO 
Very Useful. Solve my problem ….. you are the man