Internet stopped working; still connected to network

os:vista ultimate x64 w/ all updates.

my firefox & IE have suddenly stopped working (blank page; "website
found; waiting for reply" on IE and "waiting for xxxxx.com" on firefox)
.. literally. one minute they were working, the next minute they weren't.
i didn't do anything special in between. not even a reboot.

now, it's only IE and firefox; messenger still works and so does skype
and some other internet apps.
i can even ping yahoo.com from cmd.

- i've tried rebooting, no help.
- I've tried reinstalling firefox, no help.
- i've tried switching from wired connection to wireless; no help
- i've tried disabling firewall; no help.
- i've run anti-virus (nod32) and anti-malware; no help
- It's not the router or ISP, because my laptop works fine.

and finally, this problem happened to me about 4 weeks ago; i was
unable to find a solution, so i reformated and reinstalled vista! now,
it's happened again. grrrrr...


more info. i tried a system restore back to when i know my pc was
working fine. and the problem hasn't gone away.

also, new piece of info. i can connect to 192.168.0.1 (router's
web-config) through firefox and IE. So that removes the possibility of
something blocking port 80 on my PC.

tried to telnet google.co.uk 80. & that was no go.


--
istrong