Why isnt google.com, youtube.com and yahoo search webpages loading on my sony vaio notebook?

hi, I am from India. I have the sony viao notebook with windows vista os. since the last 1 month or so the following webpages do not load on any of the 3 browsers (chrome, mozilla4beta, IE):
www.google.com (though www.google.co.in loads)
www.youtube.com
yahoo search
whenever I click on the link it shows loading, but doesnt show the page n after a while the session is timed out. my internet connection works very fine. I tried pinging google.com and youtube but the result shown is 'timed out'.
i entered the IP address of google. only the home page displays, even its search results do not open.
basically, nething with www.google.com does not load.
i even deleted chrome because some sites suggested tht I try 2 download it again. now I m not getting access to it either.
pls help asap..

If other sites work normally, that could be an IP addressing or DNS server problem. It could also have something to do with support for their advertising. Contact your Internet Service Provider.