is there any chance that u are using comodo DNS servers? (by default installation of comodo firewall, it changes the DNS servers to theirs)
i remembered not too long ago, i had a problem accessing facebook/twitter while using its servers (about 1 month ago)
found out that comodo DNS server is blocking access (it has some malware blocking capabilities but something went wrong on their side)
try changing the DNS back to your broadband service provider's default primary/secondary DNS
please report back 
comodo DNS was always disabled, as it is now.
i found out that while connecting to upload.wikimedia.org with avastsvc.exe the bytes in (view by comodo firewall) is 20bytes, and it keeps like that, and it wont get more than 300bytes.
without using avastsvc.exe chrome.exe/iexplore.exe will download from upload.wikimedia.org with 65kbps
wierd huh
tried everything, even tried while comodo and sandboxie were closed = NOTHING
