Internet is working but some sites do not open

[dorje]

i have windows vista ultimate,
my router is UTstarcom WA3002G4,
the problem is that internet is working fine but some of the websites do not open at all,, very rarely they open,,
what should i do??

 

[dinek]

Firstable change your dns server to opendns...

208.67.222.222
208.67.220.220